Remove webrtc::VideoDecoder::PrefersLateDecoding.

This is just general cleanup.

The assumed behavior is late decoding, and this function is not used to make any decision (except in the deprecated jitter buffer).

Bug: webrtc:12271
Change-Id: Ifb48186d55903f068f25e44c5f73e7a724f6f456
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/200804
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Sami Kalliomäki <sakal@webrtc.org>
Reviewed-by: Christoffer Rodbro <crodbro@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32940}

modules/video_coding/generic_decoder.cc

@@ -294,8 +294,4 @@ int32_t VCMGenericDecoder::RegisterDecodeCompleteCallback(
   return decoder_->RegisterDecodeCompleteCallback(callback);
 }
 
-bool VCMGenericDecoder::PrefersLateDecoding() const {
-  return decoder_->PrefersLateDecoding();
-}
-
 }  // namespace webrtc