title: couldn't remove origin point in matplotlib polycollection
body: <p>I have tried an example with PolyCollection from matplotlib tutorials and noticed one strange thing. I couldn't remove this points from axes origin see fig. How do I manage this?</p>
  
  <p><img src="https://i.stack.imgur.com/BQonc.png" alt="enter image description here"></p>
  
  <pre><code>from mpl_toolkits.mplot3d import Axes3D
  from matplotlib.collections import PolyCollection
  from matplotlib.colors import colorConverter
  import matplotlib.pyplot as plt
  import numpy as np
  
  fig = plt.figure()
  ax = fig.gca(projection='3d')
  
  cc = lambda arg: colorConverter.to_rgba(arg, alpha=0.6)
  
  xs = np.arange(5, 10, 0.4)
  verts = []
  zs = [0.0, 1.0, 2.0, 3.0]
  for z in zs:
      ys = np.random.rand(len(xs))
      ys[0], ys[-1] = 0.1, 0
      verts.append(list(zip(xs, ys)))
  
  poly = PolyCollection(verts, facecolors = [cc('r'), cc('g'), cc('b'),
                                             cc('y')])
  poly.set_alpha(0.7)
  ax.add_collection3d(poly, zs=zs, zdir='y')
  
  ax.set_xlabel('X')
  ax.set_xlim3d(0, 10)
  ax.set_ylabel('Y')
  ax.set_ylim3d(-1, 4)
  ax.set_zlabel('Z')
  ax.set_zlim3d(0, 1)
  
  plt.show()
  </code></pre>