FIX: do not replace the Axes._children list object

Each Artist keeps a reference to `Axes._children.remove` as
`art._remove_method`.  If we replace the `_children` instance on the Axes with
a different list instance the Artists will not be updated and their remove
method will refer to the wrong list.  This will cause subsequent failures on
the next draw because on remove we reset the `art.axes` and `art.figure` to
None.

xref https://discourse.matplotlib.org/t/host-subplot-and-artist-remove/23374

Author: tacaswell

lib/mpl_toolkits/axes_grid1/parasite_axes.py

@@ -136,7 +136,7 @@ def draw(self, renderer):
             self._children.extend(ax.get_children())
 
         super().draw(renderer)
-        self._children = self._children[:orig_children_len]
+        del self._children[orig_children_len:]
 
     def clear(self):
         super().clear()

lib/mpl_toolkits/axes_grid1/tests/test_axes_grid1.py

@@ -684,3 +684,14 @@ def test_imagegrid():
     im = ax.imshow([[1, 2]], norm=mpl.colors.LogNorm())
     cb = ax.cax.colorbar(im)
     assert isinstance(cb.locator, mticker.LogLocator)
+
+
+def test_removal():
+    import matplotlib.pyplot as plt
+    import mpl_toolkits.axisartist as AA
+    fig = plt.figure()
+    ax = host_subplot(111, axes_class=AA.Axes, figure=fig)
+    col = ax.fill_between(range(5), 0, range(5))
+    fig.canvas.draw()
+    col.remove()
+    fig.canvas.draw()