Remove nodejs-6_x which is about to enter EOL

- Remove nodejs-6_x
- Set nodejs / nodejs-slim to nodejs-8_x / nodejs-slim-8_x
- Re-generate node2nix generated files using nodejs-8_x instead

pkgs/development/node-packages/composition-v6.nix

@@ -1,17 +0,0 @@
-# This file has been generated by node2nix 1.6.0. Do not edit!
-
-{pkgs ? import <nixpkgs> {
-    inherit system;
-  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-6_x"}:
-
-let
-  nodeEnv = import ./node-env.nix {
-    inherit (pkgs) stdenv python2 utillinux runCommand writeTextFile;
-    inherit nodejs;
-    libtool = if pkgs.stdenv.isDarwin then pkgs.darwin.cctools else null;
-  };
-in
-import ./node-packages-v6.nix {
-  inherit (pkgs) fetchurl fetchgit;
-  inherit nodeEnv;
-}

pkgs/development/node-packages/generate.sh

@@ -4,6 +4,5 @@
 set -eu -o pipefail
 
 rm -f node-env.nix
-node2nix -6 -i node-packages-v6.json -o node-packages-v6.nix -c composition-v6.nix
 node2nix -8 -i node-packages-v8.json -o node-packages-v8.nix -c composition-v8.nix
 node2nix --nodejs-10 -i node-packages-v10.json -o node-packages-v10.nix -c composition-v10.nix