Mojo: Remove unused hello_world_service code

mojo/examples/hello_world_service/hello_world_service_impl.h

-// 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.
-
-#ifndef MOJO_EXAMPLES_HELLO_WORLD_SERVICE_HELLO_WORLD_SERVICE_IMPL_H_
-#define MOJO_EXAMPLES_HELLO_WORLD_SERVICE_HELLO_WORLD_SERVICE_IMPL_H_
-
-#include "mojo/public/bindings/lib/remote_ptr.h"
-#include "mojom/hello_world_service.h"
-
-namespace mojo {
-namespace examples {
-
-class HelloWorldServiceImpl : public HelloWorldServiceStub {
- public:
-  explicit HelloWorldServiceImpl(ScopedMessagePipeHandle pipe);
-  virtual ~HelloWorldServiceImpl();
-  virtual void Greeting(const String& greeting) MOJO_OVERRIDE;
-
- private:
-  RemotePtr<HelloWorldClient> client_;
-};
-
-}  // namespace examples
-}  // namespace mojo
-
-#endif  // MOJO_EXAMPLES_HELLO_WORLD_SERVICE_HELLO_WORLD_SERVICE_IMPL_H_