MenuItem: Don't delete owned bound actions

They may be referenced from somewhere else, and
there's no reason not to keep them alive while
the MenuItem is alive.

Task-number: QTBUG-37554
Change-Id: Idaab616c856348c0b7eeb1a2e9fdc5bfc3f8a5fd
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
ComboBox: fix a warning in MenuContentItem

Change-Id: I8428d7e2f768cd7341ecb3efcc52fc2dba1d0ca0
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>