nixos/tests/iftop.nix: get rid of `with lib`

nixos/tests/iftop.nix

···
 import ./make-test-python.nix ({ pkgs, lib, ... }:
 
-with lib;
-
 {
   name = "iftop";
-  meta.maintainers = with pkgs.lib.maintainers; [ ma27 ];
+  meta.maintainers = with lib.maintainers; [ ma27 ];
 
   nodes = {
     withIftop = {