convert delete object and theme queryboxes to .ui

Change-Id: Id8d54c55ab1b8c7e618654874bc8b9af949ec970
Reviewed-on: https://gerrit.libreoffice.org/7245
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>