nixos/make-options-doc: deprecate docbook outputs

they're no longer necessary for us and will almost definitely start to
rot now (like commonmark and asciidoc outputs did previously). most
existing users seem to take the docbook output and run it through pandoc
to generate html, those can easily migrate to use commonmark instead.
other users will hopefully pipe up when they notice that things they rely
on are going away.

optionsUsedDocbook has only been around for one release and only exposed
to allow other places to generate warnings, so that does not deserve
such precautions.

nixos/doc/manual/default.nix

···
     '';
 
 in rec {
-  inherit (optionsDoc) optionsJSON optionsNix optionsDocBook optionsUsedDocbook;
+  inherit (optionsDoc) optionsJSON optionsNix optionsDocBook;
 
   # Generate the NixOS manual.
   manualHTML = runCommand "nixos-manual-html"

nixos/lib/make-options-doc/default.nix

···
       echo "file json-br $dst/options.json.br" >> $out/nix-support/hydra-build-products
     '';
 
-  optionsUsedDocbook = pkgs.runCommand "options-used-docbook" {} ''
-    if [ -e ${optionsJSON}/share/doc/nixos/.used-docbook ]; then
-      echo 1
-    else
-      echo 0
-    fi >"$out"
-  '';
-
-  optionsDocBook = pkgs.runCommand "options-docbook.xml" {
-    nativeBuildInputs = [
-      pkgs.nixos-render-docs
-    ];
-  } ''
-    nixos-render-docs -j $NIX_BUILD_CORES options docbook \
-      --manpage-urls ${pkgs.path + "/doc/manpage-urls.json"} \
-      --revision ${lib.escapeShellArg revision} \
-      --document-type ${lib.escapeShellArg documentType} \
-      --varlist-id ${lib.escapeShellArg variablelistId} \
-      --id-prefix ${lib.escapeShellArg optionIdPrefix} \
-      ${optionsJSON}/share/doc/nixos/options.json \
-      "$out"
-  '';
+  optionsDocBook = lib.warn "optionsDocBook is deprecated since 23.11 and will be removed in 24.05"
+    (pkgs.runCommand "options-docbook.xml" {
+      nativeBuildInputs = [
+        pkgs.nixos-render-docs
+      ];
+    } ''
+      nixos-render-docs -j $NIX_BUILD_CORES options docbook \
+        --manpage-urls ${pkgs.path + "/doc/manpage-urls.json"} \
+        --revision ${lib.escapeShellArg revision} \
+        --document-type ${lib.escapeShellArg documentType} \
+        --varlist-id ${lib.escapeShellArg variablelistId} \
+        --id-prefix ${lib.escapeShellArg optionIdPrefix} \
+        ${optionsJSON}/share/doc/nixos/options.json \
+        "$out"
+    '');
 }

nixos/modules/misc/documentation.nix

···
     (mkIf cfg.nixos.enable {
       system.build.manual = manual;
 
-      system.activationScripts.check-manual-docbook = ''
-        if [[ $(cat ${manual.optionsUsedDocbook}) = 1 ]]; then
-          echo -e "\e[31;1mwarning\e[0m: This configuration contains option documentation in docbook." \
-                  "Support for docbook is deprecated and will be removed after NixOS 23.05." \
-                  "See nix-store --read-log ${builtins.unsafeDiscardStringContext manual.optionsJSON.drvPath}"
-        fi
-      '';
-
       environment.systemPackages = []
         ++ optional cfg.man.enable manual.manpages
         ++ optionals cfg.doc.enable [ manual.manualHTML nixos-help ];