Move RtpFrameObject and EncodedFrame out of video_coding namespace.

Bug: webrtc:12579
Change-Id: Ib7ecd624eb5c54abb77fe08440a014aa1e963865
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212860
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33542}

modules/video_coding/frame_object.cc

@@ -19,7 +19,6 @@
 #include "rtc_base/checks.h"
 
 namespace webrtc {
-namespace video_coding {
 RtpFrameObject::RtpFrameObject(
     uint16_t first_seq_num,
     uint16_t last_seq_num,
@@ -128,5 +127,4 @@ const RTPVideoHeader& RtpFrameObject::GetRtpVideoHeader() const {
   return rtp_video_header_;
 }
 
-}  // namespace video_coding
 }  // namespace webrtc