coq-community projects still referencing legacy Nix infrastructure.

[Zimmi48]

As of #99, there shouldn't be any default.nix file auto-generated with the templates in coq-community projects (default.nix files generated directly with the Coq Nix Toolbox infrastructure or manually written default.nix files are fine). There should also no longer be any version_or_url fields in the meta.yml files. Here are the remaining offending repositories:

• https://github.com/coq-community/alea
• https://github.com/coq-community/almost-full
• https://github.com/coq-community/atbr
• https://github.com/coq-community/bertrand
• https://github.com/coq-community/buchberger
• https://github.com/coq-community/coq-100-theorems
• https://github.com/coq-community/coqtail-math (PR opened at support 8.14 and beyond, update CI and boilerplate coqtail-math#3)
• https://github.com/coq-community/corn
• https://github.com/coq-community/jmlcoq
• https://github.com/coq-community/lemma-overloading
• https://github.com/coq-community/math-classes
• https://github.com/coq-community/reglang (PR opened at New Nix CI setup. reglang#29)

[palmskog]

I will take care of almost-full, bertrand, buchberger, and jmlcoq.

I think we can ping @anton-trunov to fix alea and lemma-overloading. The former should be able to easily use the lightweight Nix CI (see huffman for how that is done).