and drop DestroyMenu, all the implementations just delete the object

Change-Id: I673997ea1a9c5216b100cafdc70a8f697732769b
Reviewed-on: https://gerrit.libreoffice.org/55501Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>