Revert of [Chromecast] Change chromecast_branding to public

chromecast/chromecast.gni

 # Copyright 2015 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.
 
 declare_args() {
-  # chromecast_branding is used to indicate build version. Set it to
-  # "public" for Chromium build.
-  # TODO(slan): Make this variable consistent with the GYP build.
-  chromecast_branding = "public"
+  # is_chromecast_chrome_branded is set to true for an official build
+  is_chromecast_chrome_branded = false
 
   use_playready = false
 }