Remove forcing fullscreen in KeyboardVisibilityControlTest#runImeVisibilityWhenImeTransitionBetweenActivities

because the tests are passing on latest builds even on desktop
environments.

Bug: 438635422
Test: KeyboardVisibilityControlTest#testImeVisibilityWhenImeTransitionBetweenActivities_Full
Flag: EXEMPT test fix
Change-Id: Ie4fe4ebdcc297cf5c9d22c7ad4f298dc486cd114