From Peter Thatcher:

At TPAC 2014, we realized that now that we have RtpSender, we don't need a DTMFSender to be tied to a track.  We can tie it to an RtpSender instead, and that would clean things up a fair bit.

Based on that, I propose we: 

1. Remove RTCPeerConnection.createDTMFSender
2. Add RTCRtpSender.dtmf, of type "RTCDTMFSender?".
3. Remove RTCDTMFSender.canInsertDTMF and RTCDTMFSender.track.
  
The rule is: If RtpSender.dtmf is non-null, you can send DTMF.  Here is an example:

var pc = ...;
var track = ...;
var rtpSender = pc.addTrack(track);
if (rtpSender.dtmf) {
  rtpSender.dtmf.insertDTMF(...);
}

WebRTC API bugs have been moved to github issues: https://github.com/w3c/webrtc-pc/issues

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