Drop dependency of common_video on api:libjingle_peerconnection_api.

Deleting the apparently unused include of api/rtp_headers from
common/video/include/video_frame.h broke the PayloadRouter and
VideoSendStream code under video/. Missing declaration of the
RtpPayloadState struct declared in api/rtp_headers.h. Moving the
declaration of that struct to payload_router.h (outside of the api),
since it's used only internally in video/, and that seemed to be a
more logical place for it.

Bug: webrtc:7504
Change-Id: Ibed8233dfeea8bdf144db5422cdf897da824d6ee
Reviewed-on: https://webrtc-review.googlesource.com/53701
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22080}

api/rtp_headers.h

@@ -168,11 +168,6 @@ struct RtpKeepAliveConfig final {
   bool operator!=(const RtpKeepAliveConfig& o) const { return !(*this == o); }
 };
 
-// Currently only VP8/VP9 specific.
-struct RtpPayloadState {
-  int16_t picture_id = -1;
-};
-
 }  // namespace webrtc
 
 #endif  // API_RTP_HEADERS_H_