Remove callback before WindowState removal

ViewRootImpl was removing the callback from the server after the
windowState was removed, which was consistently failing resulting in an
exception in the log.

Now the removal is done before the ViewRootImpl's window removal

Test: Manually check that the error is not appearing in the log
Bug: 226089354
Change-Id: Ie9cb9940791b16d6ae1b243079794583c87b1a5c