Destroy() client after onClientFinished.

Destroy() must be called from BaseClientMonitor in order for it to
properly unlink to death from the binder token.

For ex.

1. AuthenticationClient created.
2. AuthenticationClient linksToDeath on binder token.
3. client dies(settings or another application), long after the
onClientFinished() method has been called.
4. AuthenticationClient.onBinderDied() is invoked.
5. Cancel() being invoked on a stale cancellation signal.

Test: Verified that the destroy() signal is being sent after fp/face
authentication clients.
Test: atest FrameworksServicesTests
Bug: 193883067

Change-Id: I780e8c3a42359df3c57b469a40c25a3113ee6fd7