Remove the failed-to-launch activity if attached to a parent

An exception was unexpectedly thrown while adding a child
activity to a task. That resulted in a abnormal state that
the activity is a child of the task while the
ActivityRecord#task was still null (which is updated
until #onParentChanged being called).

The CL removes the activity from its parent if any.

Bug: 224555550
Test: wm presubmit
Test: start a standard-launch-mode activity and put
      it to background, kill its process and start the
      activity again with FLAG_ACTIVITY_CLEAR_TOP flag.
Change-Id: I30ff04d961f3ca23cef89b6a5b6977860e9792d0