Remove a gene list and links to cases.

def remove_genelist(self, list_id, case_obj=None):
        """Remove a gene list and links to cases."""
        gene_list = self.gene_list(list_id)

        if case_obj:
            # remove a single link between case and gene list
            case_ids = [case_obj.id]
        else:
            # remove all links and the list itself
            case_ids = [case.id for case in gene_list.cases]
            self.session.delete(gene_list)

        case_links = self.query(CaseGenelistLink).filter(
            CaseGenelistLink.case_id.in_(case_ids),
            CaseGenelistLink.genelist_id == gene_list.id
        )
        for case_link in case_links:
            self.session.delete(case_link)

        self.save()