title: Remove lines from color and fill legends
body: <p>I have a plot with three different legends: one for <code>linetype</code>, one for <code>color</code>, and one for <code>fill</code>. In the <code>color</code> and <code>fill</code> legends there are also some lines which I wish to remove, but how? </p>
  
  <p>Here is some example code:</p>
  
  <pre><code># some data
  hline_df &lt;- data.frame(name = c('a', 'b'), y = c(1, 2))
  df &lt;- data.frame(x = c(1, 2), y = c(0.5, 1.5), con = c('a', 'b'), col = c('d', 'e'))
  
  # the plot
  ggplot(df, aes(x, y, fill = con)) +
    geom_bar(stat = 'identity') + 
    geom_point(aes(color = col)) +
    geom_hline(data = hline_df, aes(yintercept = y, linetype = name),
               color = 'red', show_guide = TRUE)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/ho9Vz.png" alt="enter image description here"></p>
  
  <p>I get the "name" guide for both red lines, that is fine.<br>
  The "col" guide has red lines crossing the dots, I want to remove them!<br>
  The "con" guide also has red lines which should be removed.</p>
  
  <p>I could modify parts of the legend with </p>
  
  <pre><code>guides(fill = guide_legend(override.aes = list(colour = NULL)),
         color = guide_legend(override.aes = list(colour = NULL)))
  </code></pre>
  
  <p>This removes the colour, but the lines are still there.</p>
  
  <p>Thanks in advance!</p>