treewide: simplify pkgs.stdenv.lib -> pkgs.lib

The library does not depend on stdenv, that `stdenv` exposes `lib` is
an artifact of the ancient origins of nixpkgs.

nixos/tests/systemd-networkd.nix

@@ -61,7 +61,7 @@ let generateNodeConf = { lib, pkgs, config, privk, pubk, peerId, nodeId, ...}: {
     };
 in import ./make-test-python.nix ({pkgs, ... }: {
   name = "networkd";
-  meta = with pkgs.stdenv.lib.maintainers; {
+  meta = with pkgs.lib.maintainers; {
     maintainers = [ ninjatrappeur ];
   };
   nodes = {