xps-15-9560: disable broken bumblebee for now

Looks like it fails to evaluate in nixpkgs just now

dell/xps/15-9560/default.nix

@@ -1,25 +1,39 @@
-{ lib, pkgs, ... }:
-
 {
  imports = [
  ../../../common/cpu/intel
  ../../../common/cpu/intel/kaby-lake
  ../../../common/pc/laptop
  ./xps-common.nix
+
+ # FIXME: remove this when bumblebee works again
+ ../../../common/gpu/nvidia/disable.nix
  ];
 
+
+ /* Bumblebee seems to fail to evaluate:
+ (stack trace truncated; use '--show-trace' to show the full trace)
+
+ error: assertion '(useSettings -> (! libsOnly))' failed
+
+ at /home/joerg/git/nixpkgs/pkgs/os-specific/linux/nvidia-x11/generic.nix:61:1:
+
+ 60|
+ 61| assert useSettings -> !libsOnly;
+ | ^
+ 62| assert !libsOnly -> kernel != null;
+
  # This configuration makes intel default and optionaly applications could run nvidia with optirun.
  # To Optimize for your use case import intel or nvidia only configuration instead
  # xps-9560/intel
  # or
  # xps-9560/nvidia
 
 
- ##### bumblebee working, needs reboot to take affect and to use it run: optirun "<application>"
- services.xserver.videoDrivers = [ "intel" "nvidia" ];
- boot.blacklistedKernelModules = [ "nouveau" "bbswitch" ];
- boot.extraModulePackages = [ pkgs.linuxPackages.nvidia_x11 ];
- hardware.bumblebee.enable = lib.mkDefault true;
- hardware.bumblebee.pmMethod = lib.mkDefault "none";
-
+  ##### bumblebee working, needs reboot to take affect and to use it run: optirun "<application>"
+  services.xserver.videoDrivers = [ "intel" "nvidia" ];
+  boot.blacklistedKernelModules = [ "nouveau" "bbswitch" ];
+  boot.extraModulePackages = [ config.boot.kernelPackages.nvidia_x11 ];
+  hardware.bumblebee.enable = lib.mkDefault true;
+  hardware.bumblebee.pmMethod = lib.mkDefault "none";
+ */
 }