elmPackages: fix nodejs packages

Fixes regression caused by
    4c60ee3da1 (pull: #142915)
    following patch of nodePackages using nodejs-14_x
    2c3b3e69ad (pull: #149120)

    - clenups and updates in generate-node-packages.sh
    - specify nodejs version in default.nix

    This makes elmPackages.* build with nodejs-14
    which resolves the issue with npm installation failing

pkgs/development/compilers/elm/default.nix

@@ -1,10 +1,13 @@
 { lib, stdenv, pkgs
-, haskell, haskellPackages, nodejs
+, haskell, haskellPackages, nodejs-14_x
 , fetchurl, fetchpatch, makeWrapper, writeScriptBin
   # Rust dependecies
 , curl, rustPlatform, openssl, pkg-config, Security, darwin
 }:
 let
+  # To controll nodejs version we pass down
+  nodejs = nodejs-14_x;
+
   fetchElmDeps = import ./fetchElmDeps.nix { inherit stdenv lib fetchurl; };
 
   hsPkgs = haskellPackages.override {

pkgs/development/compilers/elm/packages/generate-node-packages.sh

@@ -4,9 +4,7 @@ ROOT="$(realpath "$(dirname -- "$(readlink -f -- "${BASH_SOURCE[0]}")")"/../../.
 
 set -eu -o pipefail
 
-rm -f node-env.nix
 $(nix-build $ROOT -A nodePackages.node2nix --no-out-link)/bin/node2nix \
-    --nodejs-12 \
     -i node-packages.json \
     -o node-packages.nix \
     -c node-composition.nix \