Remove channel ids from various interfaces.

Starts by removing channel/engine id from ViEChannel which propagates
down to the RTP/RTCP module as well as the transport class.

IncomingVideoStream::RenderFrame() is untouched for now but receives a
fake id instead of the previous channel id. Added a TODO to remove it
later but the RenderFrame call is implemented in a lot of
platform-dependent files and should probably remove the "manager" aspect
of renderers, so preferring to do it separately

BUG=webrtc:1695
R=henrika@webrtc.org, mflodman@webrtc.org

Review URL: https://codereview.webrtc.org/1335353005 .

Cr-Commit-Position: refs/heads/master@{#9978}

webrtc/modules/rtp_rtcp/interface/rtp_rtcp.h

@@ -57,7 +57,6 @@ class RtpRtcp : public Module {
     *  paced_sender             - Spread any bursts of packets into smaller
     *                             bursts to minimize packet loss.
     */
-    int32_t id;
     bool audio;
     bool receiver_only;
     Clock* clock;