Unbind CallScreeningService when timeout reached.

In a vulnerability, the exploiter showed that an app which implements a
service with role holding ROLE_CALL_SCREENING can be used to keep a
service alive. The assumption is that the CallScreeningService class
uses MSG_SCREEN_CALL to screen the call and results in the service being
unbound for outgoing calls once screening completes. However, a vanilla
service which holds the ROLE_CALL_SCREENING role can still be used as
the default call screening app which keeps the service alive.

This CL ensures that after the timeout is reached that we try to unbind
the service if possible.

Bug: 300904123
Test: Manual test to verify that onDestroy is called for the service
after the timeout is reached.

Change-Id: I30d276867c571ece113106d3b363fce99d64f441