Support to transfer freeform task into split screen

Clear overrided windowing mode and window bounds when a task vanished
from freeform task organizer to make sure the task can inherit config
from its new parent.

Fix: 204842882
Test: put a task in freeform, then trigger split screen with such task,
      observed it applied multi-window windowing mode and bounds
      properly.
Change-Id: Ifb100d17a83931237e58bcd774dce304a3fdb731