`bundlers` output

That old forgotten api, the [bundlers](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-bundle.html) are missing from `perSystem` 

```
{
  perSystem = {pkgs, ...}: {
    bundlers.identity = drv: drv;
  };
}

  ...
The option `perSystem.x86_64-linux.bundlers' does not exist
```