Get rid of the ability to unregister preferences.

chrome/browser/prefs/pref_service_syncable.cc

Index: chrome/browser/prefs/pref_service_syncable.cc
diff --git a/chrome/browser/prefs/pref_service_syncable.cc b/chrome/browser/prefs/pref_service_syncable.cc
index cf1ab7a54b8b22226d9c90d83da34f2da28e101a..5d26e17e37cd3c428fb6191d5da7816309e2526d 100644
--- a/chrome/browser/prefs/pref_service_syncable.cc
+++ b/chrome/browser/prefs/pref_service_syncable.cc
@@ -132,13 +132,6 @@ void PrefServiceSyncable::AddRegisteredSyncablePreference(const char* 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());