Now the crazy constructors of CommonSalLayout are gone, we can merge
the two and drop one level of indirection.

Change-Id: I166e4ed2c9d22c1ce75246d486f7526c4928f652
Reviewed-on: https://gerrit.libreoffice.org/54077Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>