TST: do not use non-baseclass methods to get renderer in tests

There in now machinery for all of the public API that takes a
renderer is input to get it from the current canvas on the root
figure.  Use that machinery instead.

Author: tacaswell

lib/matplotlib/tests/test_axes.py

@@ -8223,10 +8223,9 @@ def color_boxes(fig, ax):
     """
     fig.canvas.draw()
 
-    renderer = fig.canvas.get_renderer()
     bbaxis = []
     for nn, axx in enumerate([ax.xaxis, ax.yaxis]):
-        bb = axx.get_tightbbox(renderer)
+        bb = axx.get_tightbbox()
         if bb:
             axisr = mpatches.Rectangle(
                 (bb.x0, bb.y0), width=bb.width, height=bb.height,
@@ -8237,7 +8236,7 @@ def color_boxes(fig, ax):
 
     bbspines = []
     for nn, a in enumerate(['bottom', 'top', 'left', 'right']):
-        bb = ax.spines[a].get_window_extent(renderer)
+        bb = ax.spines[a].get_window_extent()
         spiner = mpatches.Rectangle(
             (bb.x0, bb.y0), width=bb.width, height=bb.height,
             linewidth=0.7, edgecolor="green", facecolor="none", transform=None,
@@ -8253,7 +8252,7 @@ def color_boxes(fig, ax):
     fig.add_artist(rect2)
     bbax = bb
 
-    bb2 = ax.get_tightbbox(renderer)
+    bb2 = ax.get_tightbbox()
     rect2 = mpatches.Rectangle(
         (bb2.x0, bb2.y0), width=bb2.width, height=bb2.height,
         linewidth=3, edgecolor="red", facecolor="none", transform=None,