Removes all the edges from node_a to node_b from the graph.

def delete_edge_by_nodes(self, node_a, node_b):
        """Removes all the edges from node_a to node_b from the graph."""
        node = self.get_node(node_a)

        # Determine the edge ids
        edge_ids = []
        for e_id in node['edges']:
            edge = self.get_edge(e_id)
            if edge['vertices'][1] == node_b:
                edge_ids.append(e_id)

        # Delete the edges
        for e in edge_ids:
            self.delete_edge_by_id(e)