Don't check for correct windowing mode when exiting drag resize.

Tasks can get re-parented to a non split screen stack before
notifyAppTransitionDone is called. When notifyAppTransitionDone is
called later on, it will try to update the task that was previously in a
split screen stack, by updating the drag resizing flag. However, that
flag cannot be updated since the task is no longer in a split screen
stack. This will cause a system crash.

There's no need to check the windowing mode when exiting drag resize
since there's no harm in leaving drag resize when not in split screen.

Change-Id: Ibf7e531ac5adc6c37e77e15f5d61ffb4de286998
Fixes: 111521606
Test: Steps in bug