Revert of Opus implementation of the AudioDecoderFactoryTemplate API

webrtc/api/audio_codecs/opus/audio_decoder_opus.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.
- */
-
-#ifndef WEBRTC_API_AUDIO_CODECS_OPUS_AUDIO_DECODER_OPUS_H_
-#define WEBRTC_API_AUDIO_CODECS_OPUS_AUDIO_DECODER_OPUS_H_
-
-#include <memory>
-#include <vector>
-
-#include "webrtc/api/audio_codecs/audio_decoder.h"
-#include "webrtc/api/audio_codecs/audio_format.h"
-#include "webrtc/base/optional.h"
-
-namespace webrtc {
-
-// Opus decoder API for use as a template parameter to
-// CreateAudioDecoderFactory<...>().
-//
-// NOTE: This struct is still under development and may change without notice.
-struct AudioDecoderOpus {
-  struct Config {
-    int num_channels;
-  };
-  static rtc::Optional<Config> SdpToConfig(const SdpAudioFormat& audio_format);
-  static void AppendSupportedDecoders(std::vector<AudioCodecSpec>* specs);
-  static std::unique_ptr<AudioDecoder> MakeAudioDecoder(Config config);
-};
-
-}  // namespace webrtc
-
-#endif  // WEBRTC_API_AUDIO_CODECS_OPUS_AUDIO_DECODER_OPUS_H_