Simple cleanups of AudioDecoder and AudioEncoder classes

webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc

Index: webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
diff --git a/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc b/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
index b273b18e1835055ed7b01af333636c95a8425c3b..12306d9167e66ad50ec2661b802c806f327e4816 100644
--- a/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
+++ b/webrtc/modules/audio_coding/codecs/g711/audio_decoder_pcm.cc
@@ -17,7 +17,7 @@ namespace webrtc {
 void AudioDecoderPcmU::Reset() {}
 
 size_t AudioDecoderPcmU::Channels() const {
-  return 1;
+  return num_channels_;
 }
 
 int AudioDecoderPcmU::DecodeInternal(const uint8_t* encoded,
@@ -38,14 +38,10 @@ int AudioDecoderPcmU::PacketDuration(const uint8_t* encoded,
   return static_cast<int>(encoded_len / Channels());
 }
 
-size_t AudioDecoderPcmUMultiCh::Channels() const {
-  return channels_;
-}
-
 void AudioDecoderPcmA::Reset() {}
 
 size_t AudioDecoderPcmA::Channels() const {
-  return 1;
+  return num_channels_;
 }
 
 int AudioDecoderPcmA::DecodeInternal(const uint8_t* encoded,
@@ -66,8 +62,4 @@ int AudioDecoderPcmA::PacketDuration(const uint8_t* encoded,
   return static_cast<int>(encoded_len / Channels());
 }
 
-size_t AudioDecoderPcmAMultiCh::Channels() const {
-  return channels_;
-}
-
 }  // namespace webrtc