Delete unused class MessageBufferReader

Only usage was deleted in
https://webrtc-review.googlesource.com/c/src/+/214963

Bug: chromium:1197965
Change-Id: I97e60aace294ce3780b330e0f536a443899c9175
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/215238
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33752}

rtc_base/BUILD.gn

@@ -103,7 +103,6 @@ rtc_library("rtc_base_approved") {
     "event_tracer.h",
     "location.cc",
     "location.h",
-    "message_buffer_reader.h",
     "numerics/histogram_percentile_counter.cc",
     "numerics/histogram_percentile_counter.h",
     "numerics/mod_ops.h",

rtc_base/message_buffer_reader.h

@@ -1,37 +0,0 @@
-/*
- *  Copyright 2018 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.
- */
-
-#ifndef RTC_BASE_MESSAGE_BUFFER_READER_H_
-#define RTC_BASE_MESSAGE_BUFFER_READER_H_
-
-#include "rtc_base/byte_buffer.h"
-
-namespace webrtc {
-
-// A simple subclass of the ByteBufferReader that exposes the starting address
-// of the message and its length, so that we can recall previously parsed data.
-class MessageBufferReader : public rtc::ByteBufferReader {
- public:
-  MessageBufferReader(const char* bytes, size_t len)
-      : rtc::ByteBufferReader(bytes, len) {}
-  ~MessageBufferReader() = default;
-
-  // Starting address of the message.
-  const char* MessageData() const { return bytes_; }
-  // Total length of the message. Note that this is different from Length(),
-  // which is the length of the remaining message from the current offset.
-  size_t MessageLength() const { return size_; }
-  // Current offset in the message.
-  size_t CurrentOffset() const { return start_; }
-};
-
-}  // namespace webrtc
-
-#endif  // RTC_BASE_MESSAGE_BUFFER_READER_H_