Pass SdpAudioFormat through Channel, without converting to CodecInst

webrtc/modules/audio_coding/acm2/rent_a_codec.cc

Index: webrtc/modules/audio_coding/acm2/rent_a_codec.cc
diff --git a/webrtc/modules/audio_coding/acm2/rent_a_codec.cc b/webrtc/modules/audio_coding/acm2/rent_a_codec.cc
index 678769054451a0d103a2d1e928d03f84b43d9448..f0ed3011e48c9b109551f173385bf2847ddc8744 100644
--- a/webrtc/modules/audio_coding/acm2/rent_a_codec.cc
+++ b/webrtc/modules/audio_coding/acm2/rent_a_codec.cc
@@ -87,9 +87,7 @@ rtc::Optional<SdpAudioFormat> RentACodec::NetEqDecoderToSdpAudioFormat(
     case NetEqDecoder::kDecoderG722_2ch:
       return rtc::Optional<SdpAudioFormat>(SdpAudioFormat("g722", 8000, 2));
     case NetEqDecoder::kDecoderOpus:
-      return rtc::Optional<SdpAudioFormat>(
-          SdpAudioFormat("opus", 48000, 2,
-                         std::map<std::string, std::string>{{"stereo", "0"}}));
+      return rtc::Optional<SdpAudioFormat>(SdpAudioFormat("opus", 48000, 2));
     case NetEqDecoder::kDecoderOpus_2ch:
       return rtc::Optional<SdpAudioFormat>(
           SdpAudioFormat("opus", 48000, 2,