A menu item is either a separator-menu-item% object (merely
a separator), of a labelled-menu-item<%> object; the latter
is more specifically an instance of either menu-item% (a
plain menu item), checkable-menu-item% (a checkable menu
item), or menu% (a submenu).
Removes the item from its parent. If the menu item is already deleted,
has no effect.
See also restore.
Returns the menu, popup menu, or menu bar containing the item. The
parent for a menu item is specified when the menu item is created,
and it cannot be changed.
Returns #t if the menu item is deleted from its parent,
Adds a deleted item back into its parent. The item is always restored
to the end of the parent, regardless of its original position. If the
item is not currently deleted, restore