face: remove pointless method UdpFace::handleFirstReceive

Simply call DatagramFace::receiveDatagram directly.

Change-Id: Icec976fb9f4a008d08ece56c28ac652ea615bc76
face: Cleaning up onFail EventEmitter after event is fired from Face::fail

Change-Id: I3e90ae4af6843c2cd6d24835e0d3dab98f4c94df
Refs: #1718