Correct issue with BT ICS onCallRemoved not being called.

When chaining on to the disconnectedToneFuture, thenRunAsync was
originally used.  This means when the future is completed after the
disconnect tone plays, the "update call" CompletionStage would be posted
to the main thread handler to be completed later, which means it would
happen after the unbind.

Also, in updateCall, there was a bug which would cause subsequent update
call requests after disconnect (in this case changes to the conferenceable
calls) to still update the BT ICS; we now skip that.

Finally, after we trigger the BT ICS update to inform is that the call
is disconnected, we need to delay the unbind a couple seconds (just like
we do for other ICS).  If we do not, the onCallRemoved raised in the ICS
does not get a chance to complete before the ICS is unbound.

Flag: com.android.server.telecom.flags.separately_bind_to_bt_incall_service
Fixes: 358249447
Test: Manually reproduce issue and verify that the ordering is now
synchronous and the BT ICS gets informed of the call removal.

Change-Id: Ifa02ead8b8288b318248de3bd0ef0074e9f95e5b