Discard dead MmTelFeature Binder Instances

When the phone process crashes and the IMS service is in
a separate process, there is a condition where the ImsService may
still stay unbound, but alive and not torn down. In this case,
when the phone process comes back up and tries to register new
binder callbacks, detect that the old binder callbacks are dead
and discard instead of throwing an exception.

Bug: 179217608
Test: kill phone process
Change-Id: I4fc3b6d15fe19ebaf1fc52dab92a615a761222f8