Remove make scilab
It looks like we backported this patch from Debian, who had backported it from their upstream. Debian caught up to upstream and (stopped applying the patch themselves 2017)[https://salsa.debian.org/science-team/scilab/commit/a16aec8c0aac0782a6c4c6f797c6353027cdf4f7], so this helper is not needed for Bionic/Etiona.