fix: Remove unused inherit that break with nix 2.21

[tinou98]

With latests nix (2.21) we have an error about undefined variable (even when not used)

       error: undefined variable 'system'
       at /nix/store/dnldnw2fvdx6x2vhhxh0kxkm67g3l4sx-source/flake.nix:62:36:
           61|         default = pkgs.callPackage ./pkgs/kubenix.nix {
           62|           inherit (self.packages.${system});
             |                                    ^
           63|           evalModules = self.evalModules.${pkgs.system};

It seems that this line was useless (inheriting nothing), removing it fixed the issue

[hall]

Merged the other fix submitted for this (not for any good reason, just happened to look at it first), #58. So I'll close this one. Thanks!