release-lib: forAllSupportedSystems -> forTheseSystems

I'm going to move forAllSystems from nixos/release.nix, and these
functions sound too similar while doing different things.

pkgs/top-level/release-cross.nix

@@ -75,7 +75,7 @@ in
         f (["buildPackages"] ++ path) { inherit system crossSystem; }
       );
 
-    testEqual = path: systems: forAllSupportedSystems systems (testEqualOne path);
+    testEqual = path: systems: forTheseSystems systems (testEqualOne path);
 
     mapTestEqual = lib.mapAttrsRecursive testEqual;