Removes the edge identified by "edge_id" from the graph.

def delete_edge_by_id(self, edge_id):
        """Removes the edge identified by "edge_id" from the graph."""
        edge = self.get_edge(edge_id)

        # Remove the edge from the "from node"
        # --Determine the from node
        from_node_id = edge['vertices'][0]
        from_node = self.get_node(from_node_id)

        # --Remove the edge from it
        from_node['edges'].remove(edge_id)

        # Remove the edge from the "to node"
        to_node_id = edge['vertices'][1]
        to_node = self.get_node(to_node_id)

        # --Remove the edge from it
        to_node['edges'].remove(edge_id)

        # Remove the edge from the edge list
        del self.edges[edge_id]

        self._num_edges -= 1