docs: remove empty module refs

Author: seratch

mkdocs.yml

@@ -167,15 +167,6 @@ plugins:
                     - ref/extensions/memory/dapr_session.md
                     - ref/extensions/memory/encrypt_session.md
                     - ref/extensions/memory/advanced_sqlite_session.md
-                    - Experimental Codex:
-                        - ref/extensions/experimental/codex/codex_tool.md
-                        - ref/extensions/experimental/codex/codex.md
-                        - ref/extensions/experimental/codex/codex_options.md
-                        - ref/extensions/experimental/codex/thread.md
-                        - ref/extensions/experimental/codex/thread_options.md
-                        - ref/extensions/experimental/codex/turn_options.md
-                        - ref/extensions/experimental/codex/events.md
-                        - ref/extensions/experimental/codex/items.md
         - locale: ja
           name: 日本語
           build: true