that can use std::unique_ptr, and apply it in i18npool

Change-Id: Ib410abaf73d5f392c7a7a9a322872b08c948f9e9
Reviewed-on: https://gerrit.libreoffice.org/41438Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Tested-by: Noel Grandin <noel.grandin@collabora.co.uk>