Drop flattenTreeSystem and use custom function for filtering packages

[Pacman99]

I don't think we should flatten the system because if a user doesn't make a package a derivation in pkgs/default.nix we should trust that there is a reason for doing so. So instead this drops the flattenTreeSystem reference(and switches to flake-utils master branch) and replaces its usage with a custom function filterPackages. This function filter all packages that match three conditions;

• is a derivation
• not broken
• system is supported

In that order as to not cause errors when trying to reference non-derivation meta attributes.

And then also just dump all packages into legacy packages, so everything else is still accessible. I was considering removing the packages that are already in the packages output in legacyPackages, but I don't think its necessary since nix looks to the packages output first.

[nrdxp]

The code changes are good, but for the sake of a prettier git log, the first line of a commit message should be kept under 50 chars, while subsequent lines should remain under 72 chars

[Pacman99]

The code changes are good, but for the sake of a prettier git log, the first line of a commit message should be kept under 50 chars, while subsequent lines should remain under 72 chars

fixed! I really should stop using git commit -m

[nrdxp]

It's all good. I've made the same mistake. Good work!
bors r+

[bors]

Build succeeded:

• ci/hercules/derivations
• ci/hercules/evaluation

[blaggacao]

What is this mainly motivated by (for the record)?

Is this motivated by the issues we had with flake checks & multiplatform?

[nrdxp]

some context

Also flattenTreeSystem never got merged into flake-utils and was instead closed, so if the branch ever got deleted users might be pretty upset as well.