Remove use of deprecated extraArgs in evalConfig

[ibizaman]

I see this on every run of disnixos-env and nixops:

trace: warning: The extraArgs argument to eval-config.nix is deprecated. Please set config._module.args instead.

I'm not 100% convinced the issue comes from this repo but I still saw a usage of the deprecate argument in https://github.com/svanderburg/disnixos/blob/adf4377a3849223634072771a4ebfa715f1dfcba/nix/lib.nix#L76-L80

I wanted to put up a PR but I fail to see how to follow the advice in the deprecation warning to instead set config._module.args instead: https://github.com/NixOS/nixpkgs/blob/74be9234a25ac313e637362110a35c5da9c640e3/nixos/lib/eval-config.nix#L62