The current ObjC HW encoder is implemented as a C++
webrtc::VideoEncoder. We then wrap it two times in the following way:
webrtc::VideoEncoder -> RTCVideoEncoder -> webrtc::VideoEncoder.
This was originally done to minimize the code diff when landing the
injectable encoder.
This CL removes the first wrapping and implements the ObjC HW encoder
as a RTCVideoEncoder directly. Similarly, the decoder is implemented
as a RTCVideoDecoder directly.
Based on andersc@ CL: https://codereview.webrtc.org/2978623002/.
BUG=webrtc:7924
Review-Url: https://codereview.webrtc.org/2987413002
Cr-Commit-Position: refs/heads/master@{#19255}
73c0eb5014