nixos/perlless: disable NixOS documentation

NixOS documentation seems to come at the cost of another Perl dependency, and is currently not disabled-by-default in the `perlless` profile.

Consider this dependency path before the change:

```
$ nix why-depends .#some-image /nix/store/3vq9qasxlqpyq1k95nq3s13g2m6w59ay-perl-5.40.0
/nix/store/gn02dmslv3vihbwgfajws1g3ic9fj1m0-microvm-image-1-rc1
└───/nix/store/pmwncx8ja7h65zr0z9kvjncdxkymvd82-system-path
    └───/nix/store/mahxsvm46200qb879bxpdvpmamzss21c-nixos-help
        └───/nix/store/0ni8bklq7ykmbnidys169z1s9cagkm66-nixos-help
            └───/nix/store/ybl3snmpzjhna4vh8rs4zfrrky0q7xd4-w3m-0.5.3+git20230121
                └───/nix/store/3vq9qasxlqpyq1k95nq3s13g2m6w59ay-perl-5.40.0
```

After the change:

```
$ nix why-depends .#some-image /nix/store/3vq9qasxlqpyq1k95nq3s13g2m6w59ay-perl-5.40.0
'git+file:///some/path#some-image' does not depend on '/nix/store/3vq9qasxlqpyq1k95nq3s13g2m6w59ay-perl-5.40.0'
```