Suppress "dialer crashed" notification if the crashed dialer is system

dialer.

Allow non-UI in-call services return null from onBind without penalty.
Change unit test to work with this change, fix an wrong assertion and
make sure InCallController fallback to use system dialer after default
dialer disconnected.

Bug: 163033383
Test: Manually force stop the system dialer when there's an incoming
call and see no notification. atest
TelecomUnitTests:InCallControllerTests

Change-Id: Ia6583d19a0a3f2a86e9b73cce97d4fce2b019f93