Remove experimental code fro grouping notifications from the same source.

ui/message_center/message_center.gyp

 # Copyright (c) 2012 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': [
     {
@@ skipping 55 matching lines @@
         'notification_blocker.cc',
         'notification_blocker.h',
         'notification_list.cc',
         'notification_list.h',
         'notification_types.cc',
         'notification_types.h',
         'notifier_settings.cc',
         'notifier_settings.h',
         'views/bounded_label.cc',
         'views/bounded_label.h',
-        'views/group_view.cc',
-        'views/group_view.h',
         'views/constants.h',
         'views/message_bubble_base.cc',
         'views/message_bubble_base.h',
         'views/message_center_controller.h',
         'views/message_center_bubble.cc',
         'views/message_center_bubble.h',
         'views/message_center_button_bar.cc',
         'views/message_center_button_bar.h',
         'views/message_center_view.cc',
         'views/message_center_view.h',
@@ skipping 151 matching lines @@
         # See http://crbug.com/162998#c4 for why this is needed.
         ['OS=="linux" and linux_use_tcmalloc==1', {
           'dependencies': [
             '../../base/allocator/allocator.gyp:allocator',
           ],
         }],
       ],
     },  # target_name: message_center_unittests
   ],
 }