(I'm not sure about how good are the changes from ScopedVclPtr
to non-scoped, and disposeAndClear to clear. They aren't really
needed, because of the VclReferenceBase::mbDisposed logic. But
at least they should be safe, as long as we have disposeOnce
calls in Menu's dtor.)

See also previous commits:

4433d95b
("MenuItemData now properly disposes the submenu")

89c23b4a
("Sub menus no longer need manual disposing")

Change-Id: I9d455a94590f5eec9b097947f6984f1b3e477b52