title: Plotly: Remove legend title using template
body: <p>Even after passing <code>'title':None</code> inside <code>layout.legend</code> in the template, the chart still shows a legend title, whereas it should change the default setting to no legend title.<a href="https://i.stack.imgur.com/by4Ub.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/by4Ub.png" alt="passed in template" /></a></p>
  <p>If I manually pass it though with <code>fig.update_layout()</code>, it then removes the title.</p>
  <p><a href="https://i.stack.imgur.com/Vdvps.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Vdvps.png" alt="passed separately" /></a></p>
  <p>Why is this happening and how do I change the default setting to no legend title?</p>
  <p>Here's the code to recreate the graph (The manual passing in <code>update.layout()</code> is commented out)-</p>
  <pre><code>import plotly.graph_objects as go
  import plotly.io as pio
  import plotly.express as px
  import pandas as pd
  
  pio.templates['my_theme'] = go.layout.Template({
      'layout': {'annotationdefaults': {'arrowcolor': '#2a3f5f', 'arrowhead': 0, 'arrowwidth': 1},
                 'autotypenumbers': 'strict',
                 'coloraxis': {'colorbar': {'outlinewidth': 0, 'ticks': ''}},
                 'colorscale': {'diverging': [[0, '#8e0152'], [0.1, '#c51b7d'],
                                              [0.2, '#de77ae'], [0.3, '#f1b6da'],
                                              [0.4, '#fde0ef'], [0.5, '#f7f7f7'],
                                              [0.6, '#e6f5d0'], [0.7, '#b8e186'],
                                              [0.8, '#7fbc41'], [0.9, '#4d9221'], [1,
                                              '#276419']],
                                'sequential': [[0.0, '#0d0887'],
                                               [0.1111111111111111, '#46039f'],
                                               [0.2222222222222222, '#7201a8'],
                                               [0.3333333333333333, '#9c179e'],
                                               [0.4444444444444444, '#bd3786'],
                                               [0.5555555555555556, '#d8576b'],
                                               [0.6666666666666666, '#ed7953'],
                                               [0.7777777777777778, '#fb9f3a'],
                                               [0.8888888888888888, '#fdca26'], [1.0,
                                               '#f0f921']],
                                'sequentialminus': [[0.0, '#0d0887'],
                                                    [0.1111111111111111, '#46039f'],
                                                    [0.2222222222222222, '#7201a8'],
                                                    [0.3333333333333333, '#9c179e'],
                                                    [0.4444444444444444, '#bd3786'],
                                                    [0.5555555555555556, '#d8576b'],
                                                    [0.6666666666666666, '#ed7953'],
                                                    [0.7777777777777778, '#fb9f3a'],
                                                    [0.8888888888888888, '#fdca26'],
                                                    [1.0, '#f0f921']]},
                 'colorway': [&quot;#db2b39&quot;,&quot;#3d405b&quot;,&quot;#2fbf71&quot;,&quot;#faa613&quot;,&quot;#00a6fb&quot;],
                 'font': {'color': '#2a3f5f'},
                 'geo': {'bgcolor': 'white',
                         'lakecolor': 'white',
                         'landcolor': '#E5ECF6',
                         'showlakes': True,
                         'showland': True,
                         'subunitcolor': 'white'},
                 'hoverlabel': {'align': 'left'},
                 'hovermode': 'closest',
                 'legend': {'orientation': 'v',
                            'bordercolor': '#000000',
                            'borderwidth': 0.7,
                            'itemwidth': 30,
                            'x': 0.01,
                            'y': 1.075,
                            'title': None,
                            'bgcolor':'#F6F5F4'},
                 'mapbox': {'style': 'light'},
                 'paper_bgcolor': 'white',
                 'plot_bgcolor': 'white',
                 'polar': {'angularaxis': {'gridcolor': 'white', 'linecolor': 'white', 'ticks': ''},
                           'bgcolor': '#E5ECF6',
                           'radialaxis': {'gridcolor': 'white', 'linecolor': 'white', 'ticks': ''}},
                 'scene': {'xaxis': {'backgroundcolor': '#E5ECF6',
                                     'gridcolor': 'white',
                                     'gridwidth': 2,
                                     'linecolor': 'white',
                                     'showbackground': True,
                                     'ticks': '',
                                     'zerolinecolor': 'white'},
                           'yaxis': {'backgroundcolor': '#E5ECF6',
                                     'gridcolor': 'white',
                                     'gridwidth': 2,
                                     'linecolor': 'white',
                                     'showbackground': True,
                                     'ticks': '',
                                     'zerolinecolor': 'white'},
                           'zaxis': {'backgroundcolor': '#E5ECF6',
                                     'gridcolor': 'white',
                                     'gridwidth': 2,
                                     'linecolor': 'white',
                                     'showbackground': True,
                                     'ticks': '',
                                     'zerolinecolor': 'white'}},
                 'separators':'.',
                 'shapedefaults': {'line': {'color': '#2a3f5f'}},
                 'ternary': {'aaxis': {'gridcolor': 'white', 'linecolor': 'white', 'ticks': ''},
                             'baxis': {'gridcolor': 'white', 'linecolor': 'white', 'ticks': ''},
                             'bgcolor': '#E5ECF6',
                             'caxis': {'gridcolor': 'white', 'linecolor': 'white', 'ticks': ''}},
                 'title': {'x': 0.5,
                          'font_size':30},
                 'xaxis': {'automargin': True,
                           'gridcolor': '#eeeeee',
                           'linecolor': 'white',
                           'ticks': '',
                           'title': {'standoff': 15},
                           'zerolinecolor': 'white',
                           'zerolinewidth': 2},
                 'yaxis': {'automargin': True,
                           'gridcolor': '#eeeeee',
                           'linecolor': 'white',
                           'ticks': '',
                           'title': {'standoff': 15},
                           'zerolinecolor': 'white',
                           'zerolinewidth': 2}}
  })
  
  pio.templates.default = 'my_theme'
  
  df = pd.DataFrame({'date': {27: '2020-01-28',
    28: '2020-01-29',
    29: '2020-01-30',
    30: '2020-01-31',
    31: '2020-02-01'},
   'new_cases': {27: 2651.0, 28: 589.0, 29: 2068.0, 30: 1692.0, 31: 2111.0},
   'new_cases_smoothed': {27: 717.286,
    28: 801.429,
    29: 1082.857,
    30: 1283.714,
    31: 1515.0}})
  
  fig = px.line(df, x='date', y=['new_cases','new_cases_smoothed'],title='New cases',
                color_discrete_sequence = ['#DB2B39','#0D0628'])
  fig.update_traces(hovertemplate=None)
  fig.update_layout(hovermode='x unified')#, legend=dict(title=None))
  fig.show()
  </code></pre>