WebRTC.MediaHandler: don't pass constraints to peerConnection.addStream
WebRTC.MediaHandler: don't pass constraints to peerConnection.addStream

This argument:

* was removed from the current draft WebRTC spec: https://goo.gl/yqgml3 (no. 16)
* was optional before it was removed: https://goo.gl/6n5v0I
* doesn't seem useful to applications

Also, this facilitates compatibility with WebRTC plugins (such as Temasys's)
that cause an error if the argument is passed.

josephfrazier/SIP.js,markandrus/SIP.js,onsip/SIP.js,joseph-onsip/SIP.js,Escaux/SIP.js,Voiceworks/SIP.js,ronlobo/SIP.js,onsip/SIP.js