tests.nixos-functions: don’t omit derivations on non‐Linux

Hydra can handle packages that `throw` but not attributes that
disappear depending on platform, and it seems okay for evaluation to
fail here for non‐Linux platforms.

pkgs/test/nixos-functions/default.nix

@@ -17,8 +17,7 @@ let
     versionSuffix = "test";
     label = "test";
   };
-in lib.optionalAttrs stdenv.hostPlatform.isLinux (
-  pkgs.recurseIntoAttrs {
+in pkgs.recurseIntoAttrs {
 
   nixos-test = (pkgs.nixos {
     system.nixos = dummyVersioning;
@@ -27,5 +26,4 @@ in lib.optionalAttrs stdenv.hostPlatform.isLinux (
     system.stateVersion = lib.trivial.release;
   }).toplevel;
 
-  }
-)
+}