Remove duplicated user_prefs::TestingPrefServiceSyncable

extensions/BUILD.gn

 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//extensions/features/features.gni")
 import("//testing/test.gni")
 import("//tools/grit/grit_rule.gni")
 import("//tools/grit/repack.gni")
 
 assert(enable_extensions)
 
@@ skipping 110 matching lines @@
   ]
 
   # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   deps = [
     ":extensions_resources",
     "//base",
     "//components/cast_certificate:test_support",
     "//components/guest_view/browser:test_support",
-    "//components/pref_registry:test_support",
     "//components/prefs:test_support",
+    "//components/sync_preferences:test_support",
     "//content/public/common",
     "//content/test:test_support",
     "//extensions/browser",
     "//extensions/browser/api:api_registration",
     "//extensions/common",
     "//extensions/common/api",
     "//extensions/test:extensions_features",
     "//net:test_support",
     "//testing/gmock",
     "//testing/gtest",
@@ skipping 208 matching lines @@
     "//testing/gtest",
     "//third_party/hunspell",
     "//third_party/icu",
     "//third_party/libpng",
     "//third_party/zlib",
     "//ui/base:test_support",
     "//ui/resources:ui_test_pak",
     "//ui/web_dialogs:test_support",
   ]
 }