release.nix: disable private apple sdks in release

we shouldn’t let it get into the release. This includes:

- darwin.cf-private
- darwin.osx_private_sdk
- xcode

pkgs/top-level/release.nix

@@ -126,6 +126,12 @@ let
         pandas = unix;
         scikitlearn = unix;
       };
+
+      darwin = packagePlatforms pkgs.darwin // {
+        cf-private = {};
+        osx_private_sdk = {};
+        xcode = {};
+      };
     } ));
 
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