Don't use static instance of EmergencyCallListener.

There's a couple ways to fix this, but this seemed to be the most
straightforward one. Basically, we want the values for the emergency
call listener (ie. the cached isEmergency value) to reset across
different displays of the InCall UI.

Bug: 21027909
Change-Id: I0b42873e3fa52ee2fc8ee98ee876caf31ec98883