remove x86 darwin static builds for now

[will]

currently (2023-11-29) nix flake check fails on x86 macs due to

 error: don't yet have a `targetPackages.darwin.LibsystemCross for x86_64-apple-darwin`

so only have a static package on the other platforms for now. some maybe relevant issues:

• https://github.com/NixOS/nixpkgs/pull/256590
• https://github.com/NixOS/nixpkgs/issues/180771
• https://github.com/NixOS/nixpkgs/issues/270375