PSA: No longer supporting RTP data channels in Chrome

[Taylor Brandstetter]

An issue recently came up with RTP data channels in Chrome 46. We've decided that this is a good opportunity to discontinue support for RTP data channels, since they've been deprecated for 2 years: https://groups.google.com/forum/#!msg/discuss-webrtc/y2A97iCByTU/vCA_-HHbbRYJ

If you are still using RTP data channels, you should remove the "RtpDataChannel" constraint, in order to switch to SCTP data channels.