tests: Don't use pkgs.extend. OfBorg will reject it.

The good news is that it worked as expected.

pkgs/test/nixos-functions/default.nix

@@ -8,20 +8,10 @@ lib.optionalAttrs stdenv.hostPlatform.isLinux (
       fileSystems."/".device = "/dev/null";
     }).toplevel;
 
-    nixosTest-test = let
-      # extend pkgs with an extra overlay to make sure pkgs is passed along properly to machines.
-      altPkgs = pkgs.extend (self: super: {
-        # To test pkgs in machine
-        hello_s9e8ghsi = self.hello;
-        # To test lib in test
-        lib = super.lib // { testSubject_dohra8w = "nixosTest"; };
-        # To test pkgs in test
-        dash-test_ny3dseg = "-test";
-       });
-    in altPkgs.nixosTest ({ lib, pkgs, ... }: {
-      name = "${lib.testSubject_dohra8w}${pkgs.dash-test_ny3dseg}"; # These would fail if it's the wrong pkgs or lib
+    nixosTest-test = pkgs.nixosTest ({ lib, pkgs, ... }: {
+      name = "nixosTest-test";
       machine = { pkgs, ... }: {
-        environment.systemPackages = [ pkgs.hello_s9e8ghsi ];
+        environment.systemPackages = [ pkgs.hello ];
       };
       testScript = ''
         $machine->succeed("hello");