If XPersistObject support is dropped, all this unsupported old data can go

Change-Id: I7000df307920b1b04b81cc4c436009cf6b6548e0
Reviewed-on: https://gerrit.libreoffice.org/12282
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>