Revert 138216 - [Sync] Turn notifier::PushClient into an interface

jingle/notifier/listener/push_client_observer.cc

Index: jingle/notifier/listener/push_client_observer.cc
===================================================================
--- jingle/notifier/listener/push_client_observer.cc	(revision 138220)
+++ jingle/notifier/listener/push_client_observer.cc	(working copy)
@@ -1,11 +0,0 @@
-// 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 "jingle/notifier/listener/push_client_observer.h"
-
-namespace notifier {
-
-PushClientObserver::~PushClientObserver() {}
-
-}  // namespace notifier