Fix backend_driver.py

A couple of files were removed in PR matplotlib#1918, but were accidentally re-added to `backend_driver.py` by PR matplotlib#1924.

Author: tonysyu

examples/tests/backend_driver.py

@@ -63,11 +63,14 @@
     'scatter_demo.py',
     ]
 
+files['colors'] = [
+    'color_cycle_demo.py',
+    ]
+
 files['images'] = [
     'imshow_demo.py',
     ]
 
-
 files['statistics'] = [
     'errorbar_demo.py',
     'errorbar_demo_features.py',
@@ -210,14 +213,12 @@
     'nan_test.py',
     'newscalarformatter_demo.py',
     'pcolor_demo.py',
-    'pcolor_demo2.py',
     'pcolor_log.py',
     'pcolor_small.py',
     'pie_demo2.py',
     'plotfile_demo.py',
     'polar_demo.py',
     'polar_legend.py',
-    'poormans_contour.py',
     'psd_demo.py',
     'psd_demo2.py',
     'psd_demo3.py',
@@ -246,7 +247,6 @@
     'text_rotation.py',
     'text_rotation_relative_to_line.py',
     'transoffset.py',
-    'vline_demo.py',
     'xcorr_demo.py',
     'zorder_demo.py',
     ]
@@ -257,7 +257,6 @@
     'barchart_demo.py',
     'bbox_intersect.py',
     'collections_demo.py',
-    'color_cycle.py',
     'colorbar_only.py',
     'custom_projection_example.py',
     'custom_scale_example.py',