Clear starting window request if remove is requested before it is added

It is possible the add starting window to be scheduled and a remove request
come in before it is actually added. In this case we want to prevent the
addition of the starting window by clearing the AppWindowToken.startingData.

Bug: 26659857
Change-Id: I3ef6ea81d555e81b62e894003aadcc51d281b1ad
3 files changed