media: Remove SetCdmReadyCB and CdmReadyCB (part 1).

chromecast/media/cma/decoder/cast_audio_decoder_linux.cc

Index: chromecast/media/cma/decoder/cast_audio_decoder_linux.cc
diff --git a/chromecast/media/cma/decoder/cast_audio_decoder_linux.cc b/chromecast/media/cma/decoder/cast_audio_decoder_linux.cc
index 360d945a9d88d4d53e6e25a8d189995d885c019d..237716ef6c37742e01db183b10c686dfc6682e72 100644
--- a/chromecast/media/cma/decoder/cast_audio_decoder_linux.cc
+++ b/chromecast/media/cma/decoder/cast_audio_decoder_linux.cc
@@ -91,8 +91,7 @@ class CastAudioDecoderImpl : public CastAudioDecoder {
     }
     decoder_->Initialize(
         media::DecoderConfigAdapter::ToMediaAudioDecoderConfig(config_),
-        ::media::SetCdmReadyCB(),
-        base::Bind(&CastAudioDecoderImpl::OnInitialized, self),
+        nullptr, base::Bind(&CastAudioDecoderImpl::OnInitialized, self),
         base::Bind(&CastAudioDecoderImpl::OnDecoderOutput, self));
     // Unfortunately there is no result from decoder_->Initialize() until later
     // (the pipeline status callback is posted to the task runner).