Also check for not needed forward declarations.

Change-Id: I92759f3f40d9458fd192665b39b87a78d8b97e5a
Reviewed-on: https://gerrit.libreoffice.org/53418Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>