PSA: webrtc/config.h has been moved

[mbon...@webrtc.org]

As of this CL, (landed a couple of weeks ago), the content of webrtc/config.h has been moved to webrtc/api/rtpparameters.h, webrtc/call/rtp_config.h and webrtc/call/video_config.h.

In order to update your project please consider that:

• webrtc::RtpExtension has been moved to webrtc/api/rtpparameters.h.

• webrtc::NackConfig and webrtc::UlpfecConfig have been moved to webrtc/call/rtp_config.h.

• webrtc::VideoStream and webrtc::VideoEncoderConfig have been moved to webrtc/call/video_config.h.

In the next days we are going to remove the webrtc/config.h stub header so please update your project in order to include the appropriate header.