Closes old FAB tooltip if a new one appears

If the docking tooltip needs to display,
and there's already a docking tooltip,
the original tooltip is removed.

Test: test manually by triggering the tooltip a second time while one is already displayed.
Flag: EXEMPT minor internal bugfix
Bug: 349525477
Change-Id: Ibeeb8bb8eca782227d1f5285a7975b46feb3cb8b