Revert of Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

extensions/browser/api/extensions_api_client.cc

-// 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.
-
-#include "extensions/browser/api/extensions_api_client.h"
-
-namespace extensions {
-namespace {
-
-ExtensionsAPIClient* g_instance = NULL;
-
-}  // namespace
-
-ExtensionsAPIClient::ExtensionsAPIClient() { g_instance = this; }
-
-ExtensionsAPIClient::~ExtensionsAPIClient() { g_instance = NULL; }
-
-// static
-ExtensionsAPIClient* ExtensionsAPIClient::Get() { return g_instance; }
-
-void ExtensionsAPIClient::AddAdditionalValueStoreCaches(
-    content::BrowserContext* context,
-    const scoped_refptr<SettingsStorageFactory>& factory,
-    const scoped_refptr<ObserverListThreadSafe<SettingsObserver> >& observers,
-    std::map<settings_namespace::Namespace, ValueStoreCache*>* caches) {}
-
-}  // namespace extensions