Revert "Destroy MainWindow correctly"
Revert "Destroy MainWindow correctly"

This reverts commit bd007d42566c5befb249d6f94711b55fc0ef8860.

MainWindow already has DeleteOnClose attribute set and the double
deletion cause QtMediaHub to crash on exit.

qtmediahub/sasquatch,qtmediahub/sasquatch,qtmediahub/sasquatch