Clear calling identity when requesting syncInputTransaction

The syncInputTransaction can trigger a performSurfacePlacement which
could result in a callback to the client. In that case, the calling PID
will be incorrect since we didn't clear the calling identity before
requesting the performSurfacePlacement.

Bug: 154665556
Test: Hard to reproduce. Existing tests pass
Change-Id: Id7c35d356cfc435e2de225e4e0d3979751c5c7d4