Revert back to old sort_edge_index function

Author: dferre97

GNNGraphs/src/utils.jl

@@ -41,7 +41,7 @@ are sorted first according to the `ui` and then according to `vi`.
 function sort_edge_index(u, v)
     uv = collect(zip(u, v))
     p = sortperm(uv) # isless lexicographically defined for tuples
-    return (u = u[p], v = v[p], perm = p)
+    return u[p], v[p]
 end