nixos-checkout: Only fetch the Nixpkgs repo

nixos/modules/installer/tools/nixos-checkout.nix

@@ -1,8 +1,7 @@
 # This module generates the nixos-checkout script, which replaces the
-# NixOS and Nixpkgs source trees in /etc/nixos/{nixos,nixpkgs} with
-# Git checkouts.
+# Nixpkgs source trees in /etc/nixos/nixpkgs with a Git checkout.
 
-{config, pkgs, ...}:
+{ config, pkgs, ... }:
 
 with pkgs.lib;
 
@@ -19,7 +18,7 @@ let
         if [ "$1" == "-h" ] || [ "$1" == "--help" ]; then
           echo "Usage: `basename $0` [PREFIX]. See NixOS Manual for more info."
           exit 0
-        fi        
+        fi
 
         prefix="$1"
         if [ -z "$prefix" ]; then prefix=/etc/nixos; fi
@@ -31,19 +30,14 @@ let
             nix-env -iA nixos.pkgs.git || nix-env -i git
         fi
 
-        # Move any old nixos or nixpkgs directories out of the way.
+        # Move any old nixpkgs directories out of the way.
         backupTimestamp=$(date "+%Y%m%d%H%M%S")
 
-        if [ -e nixos -a ! -e nixos/.git ]; then
-            mv nixos nixos-$backupTimestamp
-        fi
-
         if [ -e nixpkgs -a ! -e nixpkgs/.git ]; then
             mv nixpkgs nixpkgs-$backupTimestamp
         fi
 
         # Check out the NixOS and Nixpkgs sources.
-        git clone git://github.com/NixOS/nixos.git nixos
         git clone git://github.com/NixOS/nixpkgs.git nixpkgs
       '';
    };