Remove kVideoCodecUnknown from WebRTC.

There is no difference between how we handle "generic" and "unkown" codecs,
so we don't need to represent both.

Bug: webrtc:8136
Change-Id: I42b0dbc8a0bae67cc21742303c963c8dd5bde1f6
Reviewed-on: https://webrtc-review.googlesource.com/92086
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24316}
diff --git a/test/video_codec_settings.h b/test/video_codec_settings.h
index f09b0b1..dadc35c 100644
--- a/test/video_codec_settings.h
+++ b/test/video_codec_settings.h
@@ -69,9 +69,7 @@
           3 * kTestWidth * kTestHeight * 8 * kTestFrameRate / 1000 / 2;
       settings->maxBitrate = settings->startBitrate;
       return;
-    case kVideoCodecMultiplex:
-    case kVideoCodecGeneric:
-    case kVideoCodecUnknown:
+    default:
       RTC_NOTREACHED();
       return;
   }