* drop the unused ImplLayoutArgs argument
* return a std::unique_ptr<GenericSalLayout>

Change-Id: I150a2a46f67f1ffbbd3ba0ffa68f5bffb30206c8
Reviewed-on: https://gerrit.libreoffice.org/66884
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>