elm: don't import <nixpkgs>, fixes tarball job

Don't import <nixpkgs>, because that is not allowed.
Broken by https://github.com/NixOS/nixpkgs/pull/63477

cc @turboMaCk

pkgs/development/compilers/elm/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv
+{ lib, stdenv, pkgs
 , haskell, nodejs
 , fetchurl, fetchpatch, makeWrapper, writeScriptBin }:
 let
@@ -8,7 +8,7 @@ let
 
   elmNodePackages =
     import ./packages/node-composition.nix {
-      inherit nodejs;
+      inherit nodejs pkgs;
       inherit (stdenv.hostPlatform) system;
     };