Clean-up of the system shutdown code paths

ash/system/tray/default_system_tray_delegate.cc

 // Copyright 2013 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 "ash/system/tray/default_system_tray_delegate.h"
 
 #include <string>
 
 #include "ash/session/session_state_delegate.h"
 #include "ash/shell.h"
@@ skipping 137 matching lines @@
 
 void DefaultSystemTrayDelegate::ShowEnterpriseInfo() {
 }
 
 void DefaultSystemTrayDelegate::ShowSupervisedUserInfo() {
 }
 
 void DefaultSystemTrayDelegate::ShowUserLogin() {
 }
 
-void DefaultSystemTrayDelegate::ShutDown() {
-}
-
 void DefaultSystemTrayDelegate::SignOut() {
 }
 
 void DefaultSystemTrayDelegate::RequestLockScreen() {
 }
 
 void DefaultSystemTrayDelegate::RequestRestartForUpdate() {
 }
 
 void DefaultSystemTrayDelegate::GetAvailableBluetoothDevices(
@@ skipping 95 matching lines @@
 
 void DefaultSystemTrayDelegate::AddCustodianInfoTrayObserver(
     CustodianInfoTrayObserver* observer) {
 }
 
 void DefaultSystemTrayDelegate::RemoveCustodianInfoTrayObserver(
     CustodianInfoTrayObserver* observer) {
 }
 
 }  // namespace ash