Fix IME sync flicker with 3-button navigation.

With keyboard sync, the dismissal is handled by the animator. Calling
hideKeyboard() on top of that causes the two signals to conflict with
each other, resulting in the visible flicker and extra delayed hiding
animation.

Fixes: 251185052
Test: manual, see videos in the bug

Change-Id: Ic12ad304ef9e4b6a51279ce18d6c09ba93bd59be