To M56: Use ffmpeg for opus decoding, no need to maintain our decoder.

media/renderers/default_renderer_factory.cc

Index: media/renderers/default_renderer_factory.cc
diff --git a/media/renderers/default_renderer_factory.cc b/media/renderers/default_renderer_factory.cc
index 07097571e4a1aa025e5b3fa2960b7aaf6c46ca22..5ccfb7b87d51c0c4fb18ad3314507affe7050ae5 100644
--- a/media/renderers/default_renderer_factory.cc
+++ b/media/renderers/default_renderer_factory.cc
@@ -13,7 +13,6 @@
 #include "media/base/decoder_factory.h"
 #include "media/base/media_log.h"
 #include "media/filters/gpu_video_decoder.h"
-#include "media/filters/opus_audio_decoder.h"
 #include "media/renderers/audio_renderer_impl.h"
 #include "media/renderers/gpu_video_accelerator_factories.h"
 #include "media/renderers/renderer_impl.h"
@@ -53,8 +52,6 @@ ScopedVector<AudioDecoder> DefaultRendererFactory::CreateAudioDecoders(
       new FFmpegAudioDecoder(media_task_runner, media_log_));
 #endif
 
-  audio_decoders.push_back(new OpusAudioDecoder(media_task_runner));
-
   // Use an external decoder only if we cannot otherwise decode in the
   // renderer.
   if (decoder_factory_)