fdo#75757: remove inheritance to std::vector

from SvxMSDffShapeOrders.

Change-Id: Idf551f1fbde907759d6a296141e2837264dbbb10
Reviewed-on: https://gerrit.libreoffice.org/11840
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>