Motivation for this change

i spotted pkgs.elvis.meta.homepage was broken on https://repology.org/repository/nix_unstable/problems
i fixed that and had a quick look through other domain issues on that page

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.

Notes

pg_top gets its source from the same domain as its homepage, and that domain seems to have been recycled by now, it does not have a listed maintainer
i feel like updating its meta.homepage would oblige me to also fix the source and complicate this PR, so i leave that to a future interested party...
openlibm could (should?) be changed to use fetchFromGitHub and the newer repo owner name.

tag @ttuegel, @orivej and @cillianderoiste as they're listed as maintainers for some of the affected packages