... rather, it's owned by maElementList.
So, use just std::unique_ptr<SmElement> instead.

Change-Id: Id18466083535677e0f7d07f8c523b433c5e2a9ec
Reviewed-on: https://gerrit.libreoffice.org/20490Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>