zfs: 0.7.13 -> 0.8.0

Same as zfsUnstable for the moment.
We still keep the zfsUnstable expression as we likely
need it in the near future again.
Also remove spl since it is no longer needed.

nixos/modules/tasks/filesystems/zfs.nix

@@ -24,11 +24,9 @@ let
   kernel = config.boot.kernelPackages;
 
   packages = if config.boot.zfs.enableUnstable then {
-    spl = null;
     zfs = kernel.zfsUnstable;
     zfsUser = pkgs.zfsUnstable;
   } else {
-    spl = kernel.spl;
     zfs = kernel.zfs;
     zfsUser = pkgs.zfs;
   };
@@ -325,8 +323,8 @@ in
       virtualisation.lxd.zfsSupport = true;
 
       boot = {
-        kernelModules = [ "zfs" ] ++ optional (!cfgZfs.enableUnstable) "spl";
-        extraModulePackages = with packages; [ zfs ] ++ optional (!cfgZfs.enableUnstable) spl;
+        kernelModules = [ "zfs" ];
+        extraModulePackages = with packages; [ zfs ];
       };
 
       boot.initrd = mkIf inInitrd {