Get rid of the ability to unregister preferences.

chrome/browser/prefs/pref_service_syncable.cc

 // 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.
 
 #include "chrome/browser/prefs/pref_service_syncable.h"
 
 #include "base/bind.h"
 #include "base/file_path.h"
 #include "base/prefs/default_pref_store.h"
 #include "base/prefs/overlay_user_pref_store.h"
@@ skipping 114 matching lines @@
   // copies will be out of sync.
   DCHECK(!pref_service_forked_);
   PrefService::UpdateCommandLinePrefStore(cmd_line_store);
 }
 
 void PrefServiceSyncable::AddRegisteredSyncablePreference(const char* path) {
   DCHECK(FindPreference(path));
   pref_sync_associator_.RegisterPref(path);
 }
 
-void PrefServiceSyncable::RemoveRegisteredPreference(const char* path) {
-  PrefService::RemoveRegisteredPreference(path);
-
-  if (pref_sync_associator_.IsPrefRegistered(path))
-    pref_sync_associator_.UnregisterPref(path);
-}
-
 void PrefServiceSyncable::OnIsSyncingChanged() {
   FOR_EACH_OBSERVER(PrefServiceSyncableObserver, observer_list_,
                     OnIsSyncingChanged());
 }