Motivation for this change

The foswiki package is badly out of date and it is time to deprecate httpd.extraSubservices in favor of real modules. Since this package is so badly out of date no one should be using it so it is acceptable to simply drop the package/subservice instead of replacing it with a module. That being said... if anyone is motivated enough to create a foswiki module I'm sure that would be welcome.

For prior work on the topic of deprecating httpd.extraSubservices see:

• limesurvey: 2.05_plus_141210 -> 3.17.1+190408, init module #57752
• wordpress: create module to replace the httpd subservice #62175
• nixos/mediawiki: init service to replace httpd subservice #62748
• drop unmaintained phabricator package, service, and httpd subservice #63100
• nixos/zabbix: overhaul package & module #63844

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• 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 nix-review --run "nix-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)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.