Mojo C++ bindings: remove some usage of AssociatedGroup from user code.

services/ui/ws/test_server_window_delegate.cc

 // Copyright 2014 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 "services/ui/ws/test_server_window_delegate.h"
 
 #include "services/ui/ws/server_window.h"
 
 namespace ui {
 namespace ws {
 
 TestServerWindowDelegate::TestServerWindowDelegate() {}
 
 TestServerWindowDelegate::~TestServerWindowDelegate() {}
 
 cc::mojom::DisplayCompositor* TestServerWindowDelegate::GetDisplayCompositor() {
   return nullptr;
 }
 
-mojo::AssociatedGroup*
-TestServerWindowDelegate::GetDisplayCompositorAssociatedGroup() {
-  return nullptr;
-}
-
 ServerWindow* TestServerWindowDelegate::GetRootWindow(
     const ServerWindow* window) {
   return root_window_;
 }
 
 }  // namespace ws
 }  // namespace ui