mathics: remove package, module and test

[flokli]

The mathics package has been broken for quite some time, uses python 2, and the required django version is long gone as well. Remove the package, module and the test (which still uses the perl test driver)

Fixes #80055

Motivation for this change

#72828

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[benley]

This is OK by me, I haven't used mathics for a long time now. I'm sure it can be resurrected if anyone really misses it.

[benley]

...that said, it looks like mathics itself is not unmaintained. The current upstream repo supports up to django 1.11 and requires python >= 3.3, so we could make it work again pretty easily if anyone wants it.

[flokli]

Let's remove it for now - we can always revert if someone takes up maintainership.