Check that all edge nodes exist in local subset.

def chk_edges(self):
        """Check that all edge nodes exist in local subset."""
        goids = set(self.go2obj)
        self.chk_edges_nodes(self.edges, goids, "is_a")
        for reltype, edges in self.edges_rel.items():
            self.chk_edges_nodes(edges, goids, reltype)