Revert canShowRotationButton() check related to mTaskBarVisible

mTaskBarVisible isn't related to immersive mode. Rather it's tied to whether we show task bar or hotseat (e.g. on the home screen).

Fixes: 272164624
Test: Open townhall. Fold and then unfold. Tilt the device and make sure the floating rotation button shows.
Change-Id: Ie8a7c617ece45509c5d069741cdee7e3037130f8