The code relied on the idea that the order-key resync that occurs after deletion would change the order keys and thus cause
a redisplay. But since both the editor and mixer can initiate an order-key resync, the other window's resync will actually
do nothing (the order keys will already be correct). This led to the incorrect placement of material in the tracks canvas,
because the first resync triggered a redisplay while the route still existed, and then the second resync didn't cause a
redisplay (repositioning) but the canvas elements representing the track went away.
Fixed by forcing a redisplay in both editor and mixer if a route deletion is believed to be triggering a row deletion
in their underlying data models.
