Revert of Loosening the coupling between WebRTC and //third_party/protobuf

webrtc/base/protobuf_utils.h

-/*
- *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include <string>
-
-#ifndef WEBRTC_BASE_PROTOBUF_UTILS_H_
-#define WEBRTC_BASE_PROTOBUF_UTILS_H_
-
-namespace webrtc {
-
-using ProtoString = std::string;
-
-}  // namespace webrtc
-
-#if WEBRTC_ENABLE_PROTOBUF
-
-#include "third_party/protobuf/src/google/protobuf/message_lite.h"
-#include "third_party/protobuf/src/google/protobuf/repeated_field.h"
-
-namespace webrtc {
-
-using google::protobuf::MessageLite;
-using google::protobuf::RepeatedPtrField;
-
-}  // namespace webrtc
-
-#endif  // WEBRTC_ENABLE_PROTOBUF
-
-#endif  // WEBRTC_BASE_PROTOBUF_UTILS_H_