Stop signal info tone when call is disconnected.

As a follow up to the CL: ag/545703, re-adding the phone disconnection
event handling in CallStateMonitor so that we can stop any signal tones
that we may have started on a call disconnect in CallNotifier.

BUG: 22834581
Change-Id: I012fe7ca9f5191807f4252db26b423feb4a30524
2 files changed