Close leaked windows when trying to preserve main one

When app has several windows and activity is relaunched + we try to preserve
main window - other windows just stayed around until removed by timeout or
replaced by app. There was a problem when one of the windows registered
broadcast receiver and set its own timer to remove it. In this case all
receivers were removed by framework because windows were considered leaked
and apps' timer caused crash when trying to remove registered receiver.

This CL removes all windows expect the main one, which we're trying to
preserve in this case.

Bug: 28337135
Change-Id: Ib8790cc8c61801f11d871ba3803bb0ebc3d3be01