nixos/brightnessctl: Remove the module

Due to the support of the systemd-logind API the udev rules aren't
required anymore which renders this module useless [0].
Note: brightnessctl should now require a working D-Bus setup and a valid
local logind session for this to work.

[0]: https://github.com/NixOS/nixpkgs/pull/79663

nixos/modules/rename.nix

@@ -42,6 +42,12 @@ with lib;
       instead, or any other display manager in NixOS as they all support auto-login.
     '')
     (mkRemovedOptionModule [ "services" "dnscrypt-proxy" ] "Use services.dnscrypt-proxy2 instead")
+    (mkRemovedOptionModule ["hardware" "brightnessctl" ] ''
+      The brightnessctl module was removed because newer versions of
+      brightnessctl don't require the udev rules anymore (they can use the
+      systemd-logind API). Instead of using the module you can now
+      simply add the brightnessctl package to environment.systemPackages.
+    '')
 
     # Do NOT add any option renames here, see top of the file
   ];