nixos/all-tests: Rely on general hydraPlatforms override

It is documented to be about `hydra.nixos.org`, so this is actually
acceptable.
If your own hydra can do it, you may set `meta.hydraPlatforms` in
your tests if you want that. (e.g. set it in a common module that's
imported in all your tests)

nixos/tests/all-tests.nix

@@ -90,22 +90,12 @@ let
 
   inherit
     (rec {
-
-      metaModule = {
-        _file = "${__curPos.file}##metaModule";
-        meta = {
-          # Infra issue: virtualization on darwin doesn't seem to work yet.
-          hydraPlatforms = platforms.linux;
-        };
-      };
-
       doRunTest =
         arg:
         ((import ../lib/testing-python.nix { inherit system pkgs; }).evalTest {
           imports = [
             arg
             readOnlyPkgs
-            metaModule
           ];
         }).config.result;
       findTests =