[bindings] Use |PostMessage| attribute for Client.postMessage to eliminate custom bindings

Source/bindings/modules/v8/custom/V8ClientCustom.cpp

Index: Source/bindings/modules/v8/custom/V8ClientCustom.cpp
diff --git a/Source/bindings/modules/v8/custom/V8ClientCustom.cpp b/Source/bindings/modules/v8/custom/V8ClientCustom.cpp
deleted file mode 100644
index cdeca9450cbaf40a4b7631e4edda50bd768d4c4e..0000000000000000000000000000000000000000
--- a/Source/bindings/modules/v8/custom/V8ClientCustom.cpp
+++ /dev/null
@@ -1,19 +0,0 @@
-// 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 "config.h"
-#include "bindings/modules/v8/V8Client.h"
-
-#include "bindings/core/v8/PostMessage.h"
-#include "bindings/core/v8/V8Binding.h"
-
-namespace blink {
-
-// FIXME: This stub should be replaced by generated code.
-void V8Client::postMessageMethodCustom(const v8::FunctionCallbackInfo<v8::Value>& info)
-{
-    postMessageMethodCommon("ServiceWorkerClient", V8Client::toImpl(info.Holder()), info);
-}
-
-} // namespace blink