nixos/dokuwiki: Drop deprecated old interface

[onny]

Motivation for this change

This PR drops the old deprecated interface used before NixOS 21.11. The syntax services.dokuwiki."hostname.local" was changed to services.dokuwiki.sites."hostname.local"`. A deprecation notice was added to the NixOS 21.11 release notes.
It would be good to drop the old interface to cleanup the Dokuwiki module with NixOS 22.05.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[happysalada]

Should we not add a note in the release notes ?

[onny]

Thanks for the review, added a note to the release notes

[happysalada]

@NinjaTrappeur you were using this if I remember correcty. This looks good to me to merge.
I'm going to wait a couple more days in case you have time to have a look.

[picnoir]

Hey, I'm not using this module anymore. Thanks for the heads up though :)