[Extensions] Remove unused parts of the preferencesPrivate API

chrome/browser/extensions/api/preferences_private/preferences_private_api.h

-// 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.
-
-#ifndef CHROME_BROWSER_EXTENSIONS_API_PREFERENCES_PRIVATE_PREFERENCES_PRIVATE_API_H_
-#define CHROME_BROWSER_EXTENSIONS_API_PREFERENCES_PRIVATE_PREFERENCES_PRIVATE_API_H_
-
-#include "base/macros.h"
-#include "chrome/browser/extensions/chrome_extension_function.h"
-#include "components/sync_driver/sync_service_observer.h"
-#include "extensions/browser/extension_function.h"
-
-namespace extensions {
-
-class PreferencesPrivateGetSyncCategoriesWithoutPassphraseFunction
-    : public ChromeAsyncExtensionFunction,
-      public sync_driver::SyncServiceObserver {
- public:
-  DECLARE_EXTENSION_FUNCTION(
-      "preferencesPrivate.getSyncCategoriesWithoutPassphrase",
-      PREFERENCESPRIVATE_GETSYNCCATEGORIESWITHOUTPASSPHRASE)
-
-  PreferencesPrivateGetSyncCategoriesWithoutPassphraseFunction();
-
- protected:
-  ~PreferencesPrivateGetSyncCategoriesWithoutPassphraseFunction() override;
-
- private:
-  // sync_driver::SyncServiceObserver:
-  void OnStateChanged() override;
-
-  // ExtensionFunction:
-  bool RunAsync() override;
-
-  DISALLOW_COPY_AND_ASSIGN(
-      PreferencesPrivateGetSyncCategoriesWithoutPassphraseFunction);
-};
-
-}  // namespace extensions
-
-#endif  // CHROME_BROWSER_EXTENSIONS_API_PREFERENCES_PRIVATE_PREFERENCES_PRIVATE_API_H_