move default.nix to shell.nix

node_environment/default.nix

@@ -1,19 +0,0 @@
-with import <nixpkgs> {};
-
-stdenv.mkDerivation {
-  name = "myNodeEnv";
-  buildInputs = with pkgs; [
-    nodejs
-  ];
-  src = null;
-  shellHook = ''
-    mkdir -p .npm
-    if [ -s global_packages.txt ]; then
-      cat global_packages.txt | xargs npm install -g --prefix $PWD/.npm
-    fi
-    if [ -s package.json ]; then
-      npm install
-    fi
-    export PATH=$PWD/.npm/bin:$PATH
-  '';
-}