Delete deprecated synced notifications code

chrome/common/extensions/api/_api_features.json

 // Copyright (c) 2012 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.
 
 // This features file defines extension APIs implemented under src/chrome.
 // See extensions/common/features/* to understand this file, in particular
 // feature.h, simple_feature.h, and base_feature_provider.h.
 //
 // Note that specifying "web_page", "blessed_web_page", or "all" as a context
 // type will require manually updating chrome/renderer/resources/dispatcher.cc.
@@ skipping 594 matching lines @@
     "contexts": ["blessed_extension"]
   },
   "streamsPrivate": {
     "dependencies": ["permission:streamsPrivate"],
     "contexts": ["blessed_extension"]
   },
   "syncFileSystem": {
     "dependencies": ["permission:syncFileSystem"],
     "contexts": ["blessed_extension"]
   },
-  "syncedNotificationsPrivate": {
-    "contexts": ["blessed_extension"],
-    "dependencies": ["permission:syncedNotificationsPrivate"]
-  },
   "systemIndicator": {
     "dependencies": ["manifest:system_indicator"],
     "contexts": ["blessed_extension"]
   },
   "systemPrivate": {
     "dependencies": ["permission:systemPrivate"],
     "contexts": ["blessed_extension"]
   },
   "tabCapture": {
     "dependencies": ["permission:tabCapture"],
@@ skipping 79 matching lines @@
     "internal": true,
     "channel": "stable",
     "dependencies": ["permission:webview"],
     "contexts": ["blessed_extension"]
   },
   "windows": {
     "dependencies": ["api:tabs"],
     "contexts": ["blessed_extension"]
   }
 }