Remove WebRtcVideoEngine::default_codec_format().
Remove WebRtcVideoEngine::default_codec_format().

R=pthatcher@webrtc.org
BUG=1788

Review URL: https://webrtc-codereview.appspot.com/24399004

Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 9f341283f64d9b905c3883fd23988eb3d5fdcb8f

sippet/talk,sippet/talk,sippet/talk,sippet/talk,sippet/talk