[Extensions] Remove unused parts of the preferencesPrivate API

chrome/chrome_browser_extensions.gypi

 # Copyright (c) 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': {
     'chrome_browser_extensions_chromeos_sources': [
       'browser/extensions/api/cast_devices_private/cast_devices_private_api.cc',
       'browser/extensions/api/cast_devices_private/cast_devices_private_api.h',
       'browser/extensions/api/certificate_provider/certificate_provider_api.cc',
@@ skipping 413 matching lines @@
       'browser/extensions/api/preference/chrome_direct_setting.cc',
       'browser/extensions/api/preference/chrome_direct_setting.h',
       'browser/extensions/api/preference/chrome_direct_setting_api.cc',
       'browser/extensions/api/preference/chrome_direct_setting_api.h',
       'browser/extensions/api/preference/preference_api.cc',
       'browser/extensions/api/preference/preference_api.h',
       'browser/extensions/api/preference/preference_api_constants.cc',
       'browser/extensions/api/preference/preference_api_constants.h',
       'browser/extensions/api/preference/preference_helpers.cc',
       'browser/extensions/api/preference/preference_helpers.h',
-      'browser/extensions/api/preferences_private/preferences_private_api.cc',
-      'browser/extensions/api/preferences_private/preferences_private_api.h',
       'browser/extensions/api/principals_private/principals_private_api.cc',
       'browser/extensions/api/principals_private/principals_private_api.h',
       'browser/extensions/api/proxy/proxy_api.cc',
       'browser/extensions/api/proxy/proxy_api.h',
       'browser/extensions/api/proxy/proxy_api_constants.cc',
       'browser/extensions/api/proxy/proxy_api_constants.h',
       'browser/extensions/api/proxy/proxy_api_helpers.cc',
       'browser/extensions/api/proxy/proxy_api_helpers.h',
       'browser/extensions/api/resources_private/resources_private_api.cc',
       'browser/extensions/api/resources_private/resources_private_api.h',
@@ skipping 719 matching lines @@
           ],
         }, {  # use_brlapi==0
           'sources': [
             'browser/extensions/api/braille_display_private/braille_controller_stub.cc',
           ],
         }],
       ],
     },
   ],
 }