Freeup lock when IME is set inactive and unbound

Any pending windowGainedFocus future should be cancelled when IME is
switched/unbound.
Additinally, startInputInner() inside synchronized block blocked
WINDOW_FOCUS_GAIN from executing. Its fine to remove synchronization
here since startInputInner() already has relevant synchronized blocks.

Change-Id: I98cb044d8cbfb80480312a3923f168aefa9b7e7d
Fix: 144103599
Bug: 139806621
Test: Manually using the steps in bug.