Disable cached-nix-shell temporarily

Until xzfc/cached-nix-shell#2 is addressed.

default.nix

@@ -35,6 +35,13 @@ device:
     };
   };
 
+  environment.systemPackages = with pkgs; [
+    # cached-nix-shell, for instant nix-shell scripts
+    # (callPackage
+    #   (builtins.fetchTarball
+    #     https://github.com/xzfc/cached-nix-shell/archive/master.tar.gz) {})
+  ];
+
   # This value determines the NixOS release with which your system is to be
   # compatible, in order to avoid breaking some software such as database
   # servers. You should change this only after NixOS release notes say you

machines/default.nix

@@ -21,10 +21,6 @@
     exfat
     ntfs3g
     hfsprogs
-    # cached-nix-shell, for instant nix-shell scripts
-    (callPackage
-      (builtins.fetchTarball
-        https://github.com/xzfc/cached-nix-shell/archive/master.tar.gz) {})
   ];
 
   ###