Remove extension-to-component migration mechanism

chrome/browser/extensions/BUILD.gn

 # 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.
 
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//chrome/common/features.gni")
 import("//extensions/features/features.gni")
 import("//media/media_options.gni")
 import("//rlz/features/features.gni")
@@ skipping 502 matching lines @@
     "chrome_requirements_checker.cc",
     "chrome_requirements_checker.h",
     "chrome_url_request_util.cc",
     "chrome_url_request_util.h",
     "clipboard_extension_helper_chromeos.cc",
     "clipboard_extension_helper_chromeos.h",
     "component_extensions_whitelist/whitelist.cc",
     "component_extensions_whitelist/whitelist.h",
     "component_loader.cc",
     "component_loader.h",
-    "component_migration_helper.cc",
-    "component_migration_helper.h",
     "context_menu_matcher.cc",
     "context_menu_matcher.h",
     "convert_user_script.cc",
     "convert_user_script.h",
     "convert_web_app.cc",
     "convert_web_app.h",
     "crx_installer.cc",
     "crx_installer.h",
     "data_deleter.cc",
     "data_deleter.h",
@@ skipping 657 matching lines @@
       "api/braille_display_private/brlapi_connection.cc",
       "api/braille_display_private/brlapi_connection.h",
       "api/braille_display_private/brlapi_keycode_map.cc",
       "api/braille_display_private/brlapi_keycode_map.h",
     ]
     deps += [ "//build/linux/libbrlapi" ]
   } else {
     sources += [ "api/braille_display_private/braille_controller_stub.cc" ]
   }
 }