Refactor RtpVideoStreamReceiver without RtpReceiver.

Bug: webrtc:7135
Change-Id: Iabf3330e579b892efc160683f9f90efbf6ff9a40
Reviewed-on: https://webrtc-review.googlesource.com/92398
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24232}

modules/rtp_rtcp/source/rtp_format.cc

@@ -54,11 +54,8 @@ RtpDepacketizer* RtpDepacketizer::Create(VideoCodecType type) {
       return new RtpDepacketizerVp8();
     case kVideoCodecVP9:
       return new RtpDepacketizerVp9();
-    case kVideoCodecGeneric:
-      return new RtpDepacketizerGeneric();
     default:
-      RTC_NOTREACHED();
+      return new RtpDepacketizerGeneric();
   }
-  return nullptr;
 }
 }  // namespace webrtc