Clean up video_coding namespace snipets.

Bug: webrtc:12579
Change-Id: I487fe017f30746e2fe83a122123b236295d96d28
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212962
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33558}

api/video/encoded_frame.h

@@ -59,11 +59,6 @@ class EncodedFrame : public webrtc::VCMEncodedFrame {
   int64_t id_ = -1;
 };
 
-// TODO(bugs.webrtc.org/12579): Remove when downstream has been updated.
-namespace video_coding {
-using ::webrtc::EncodedFrame;
-}  // namespace video_coding
-
 }  // namespace webrtc
 
 #endif  // API_VIDEO_ENCODED_FRAME_H_