Remove Sync JS generic request/reply framework

sync/js/js_reply_handler.h

-// 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.
-
-#ifndef SYNC_JS_JS_REPLY_HANDLER_H_
-#define SYNC_JS_JS_REPLY_HANDLER_H_
-
-// See README.js for design comments.
-
-#include <string>
-
-namespace syncer {
-
-class JsArgList;
-
-// An interface for objects that handle Javascript message replies
-// (e.g., WebUIs).
-class JsReplyHandler {
- public:
-  virtual void HandleJsReply(
-      const std::string& name, const JsArgList& args) = 0;
-
- protected:
-  virtual ~JsReplyHandler() {}
-};
-
-}  // namespace syncer
-
-#endif  // SYNC_JS_JS_REPLY_HANDLER_H_