[Extensions] Remove unused parts of the preferencesPrivate API

chrome/chrome_tests.gypi

 # Copyright 2013 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': {
     'build_angle_deqp_tests%': 0,
     'chrome_browser_extensions_test_support_sources': [
       # A list of sources which is shared between different browser tests.
       'browser/apps/app_browsertest_util.cc',
       'browser/apps/app_browsertest_util.h',
@@ skipping 168 matching lines @@
       'browser/extensions/api/module/module_apitest.cc',
       'browser/extensions/api/music_manager_private/music_manager_private_browsertest.cc',
       'browser/extensions/api/networking_config_chromeos_apitest_chromeos.cc',
       'browser/extensions/api/notification_provider/notification_provider_apitest.cc',
       'browser/extensions/api/omnibox/omnibox_api_browsertest.cc',
       'browser/extensions/api/page_capture/page_capture_apitest.cc',
       'browser/extensions/api/passwords_private/passwords_private_apitest.cc',
       'browser/extensions/api/permissions/permissions_apitest.cc',
       'browser/extensions/api/platform_keys/platform_keys_apitest_nss.cc',
       'browser/extensions/api/preference/preference_apitest.cc',
-      'browser/extensions/api/preferences_private/preferences_private_apitest.cc',
       'browser/extensions/api/processes/processes_apitest.cc',
       'browser/extensions/api/proxy/proxy_apitest.cc',
       'browser/extensions/api/resources_private/resources_private_apitest.cc',
       'browser/extensions/api/screenlock_private/screenlock_private_apitest.cc',
       'browser/extensions/api/sessions/sessions_apitest.cc',
       'browser/extensions/api/settings_overrides/settings_overrides_browsertest.cc',
       'browser/extensions/api/settings_private/settings_private_apitest.cc',
       'browser/extensions/api/socket/socket_apitest.cc',
       'browser/extensions/api/storage/settings_apitest.cc',
       'browser/extensions/api/streams_private/streams_private_apitest.cc',
@@ skipping 3335 matching lines @@
             'browser',
           ],
           'sources': [
             'tools/service_discovery_sniffer/service_discovery_sniffer.cc',
             'tools/service_discovery_sniffer/service_discovery_sniffer.h',
           ],
         }]
     }],
   ],  # 'conditions'
 }