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/emacs-daemon.nix

@@ -1,6 +1,6 @@
 import ./make-test-python.nix ({ pkgs, ...} : {
   name = "emacs-daemon";
-  meta = with pkgs.stdenv.lib.maintainers; {
+  meta = with pkgs.lib.maintainers; {
     maintainers = [ ];
   };