deprecate or maintain nix from this repo

[gianarb]

Hello

Do we have a guideline about nix in this repo and overall in the tinkerbell
ecosystem?

I see there are still a couple of nix files in the various repo, I did not
check out of the playground but this one looks pretty old and unmaintained.

I use Nix but I don't think it makes sense to maintain something that we do use
or want to keep up to date. What's the guideline here? Should we just remove it from the repo?