tests/nixos: don't pass in self

The reference to the flake is used in a single place only to get the
`doc` output of Lix. Remove it so that we can also instantiate the tests
in a legacy Hydra jobset (happening further down the chain).

Change-Id: Ie3eccf42d67c81fcf991342097783e5067d512bc

flake.nix

@@ -405,7 +405,6 @@
         tests =
           import ./tests/nixos {
             inherit
-              self
               lib
               nixpkgs
               nixpkgsFor

releng/local/default.nix

@@ -1,6 +1,4 @@
 {
-  self,
-  system,
   pkgs,
   ...
 }:
@@ -11,7 +9,7 @@ let
     inherit (pkgs.writers) writePython3Bin;
   };
 
-  build = self.release-jobs.all.build.${system}.doc;
+  build = pkgs.nix.doc;
 
   pythonPackages = (
     p: [

tests/nixos/default.nix

@@ -1,5 +1,4 @@
 {
-  self,
   lib,
   nixpkgs,
   nixpkgsFor,
@@ -40,7 +39,6 @@ let
       };
       _module.args.nixpkgs = nixpkgs;
       _module.args.system = system;
-      _module.args.self = self;
     })
     // {
       # allow running tests against older nix versions via `nix eval --apply`