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/hocker-fetchdocker/default.nix

@@ -1,6 +1,6 @@
 import ../make-test-python.nix ({ pkgs, ...} : {
   name = "test-hocker-fetchdocker";
-  meta = with pkgs.stdenv.lib.maintainers; {
+  meta = with pkgs.lib.maintainers; {
     maintainers = [ ixmatus ];
     broken = true; # tries to download from registry-1.docker.io - how did this ever work?
   };