XCB: send leave event on grab

When a popup is opened it grabs the input, but the leave event to the other
windows needs to be sent.

Remove the popupEnterLeave test as it did not test any code. The Popup
never gets any enter or leave events so it will succeed always succeed

Task-number: QTBUG-36862
Change-Id: I625c616eeb74b5168af7b751485e2a9a53b76cd3
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>