Removes duplicate edges from an undirected graph.

def remove_duplicate_edges_undirected(udg):
    """Removes duplicate edges from an undirected graph."""
    # With undirected edges, we need to hash both combinations of the to-from node ids, since a-b and b-a are equivalent
    # --For aesthetic, we sort the edge ids so that lower edges ids are kept
    lookup = {}
    edges = sorted(udg.get_all_edge_ids())
    for edge_id in edges:
        e = udg.get_edge(edge_id)
        tpl_a = e['vertices']
        tpl_b = (tpl_a[1], tpl_a[0])
        if tpl_a in lookup or tpl_b in lookup:
            udg.delete_edge_by_id(edge_id)
        else:
            lookup[tpl_a] = edge_id
            lookup[tpl_b] = edge_id