Move check for number_of_cores parameter validitity

from runtime check in proxy classes that picks decoder (VCMDecoderDataBase)
to a DCHECK in the VideoDecoder::Settings

Bug: None
Change-Id: Ic8c2e971486a3a7eb247f9d03815aba5ca5a7bad
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/228644
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34761}

modules/video_coding/video_coding_impl.h

@@ -59,7 +59,7 @@ class VideoReceiver : public Module {
   VideoReceiver(Clock* clock, VCMTiming* timing);
   ~VideoReceiver() override;
 
-  bool RegisterReceiveCodec(uint8_t payload_type,
+  void RegisterReceiveCodec(uint8_t payload_type,
                             const VideoDecoder::Settings& settings);
 
   void RegisterExternalDecoder(VideoDecoder* externalDecoder,