Remove views::SingleSplitView as it's presently unused.

ui/views/examples/examples.gyp

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       # GN version: //ui/views/examples
@@ skipping 24 matching lines @@
       'sources': [
         # Note: sources list duplicated in GN build.
         'bubble_example.cc',
         'bubble_example.h',
         'button_example.cc',
         'button_example.h',
         'checkbox_example.cc',
         'checkbox_example.h',
         'combobox_example.cc',
         'combobox_example.h',
-        'double_split_view_example.cc',
-        'double_split_view_example.h',
         'example_base.cc',
         'example_base.h',
         'example_combobox_model.cc',
         'example_combobox_model.h',
         'examples_window.cc',
         'examples_window.h',
         'label_example.cc',
         'label_example.h',
         'link_example.cc',
         'link_example.h',
         'menu_example.cc',
         'menu_example.h',
         'message_box_example.cc',
         'message_box_example.h',
         'multiline_example.cc',
         'multiline_example.h',
         'progress_bar_example.cc',
         'progress_bar_example.h',
         'radio_button_example.cc',
         'radio_button_example.h',
         'scroll_view_example.cc',
         'scroll_view_example.h',
-        'single_split_view_example.cc',
-        'single_split_view_example.h',
         'slider_example.cc',
         'slider_example.h',
         'tabbed_pane_example.cc',
         'tabbed_pane_example.h',
         'table_example.cc',
         'table_example.h',
         'text_example.cc',
         'text_example.h',
         'textfield_example.cc',
         'textfield_example.h',
@@ skipping 115 matching lines @@
           },
           'dependencies': [
             '../../../sandbox/sandbox.gyp:sandbox',
             '../../../content/content.gyp:sandbox_helper_win',
           ],
         }],
       ],
     },  # target_name: views_examples_with_content_exe
   ],
 }