refactor: remove unused DELETE /chats/{id}/tags/all endpoint (#24785)

The bulk-clear-chat-tags endpoint's only frontend wrapper,
deleteTagsById in src/lib/apis/chats/index.ts, is dead: nothing imports
or calls it, the path is referenced nowhere else, and the route handler
has no internal caller. Removes the route handler, the dead wrapper, and
the now-orphaned Chats.delete_all_tags_by_id_and_user_id model method
(its sole caller was this route). The shared
Chats.delete_orphan_tags_for_user method is untouched.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/open_webui/models/chats.py

@@ -1514,20 +1514,6 @@ class ChatTable:
         except Exception:
             return False
 
-    async def delete_all_tags_by_id_and_user_id(self, id: str, user_id: str, db: AsyncSession | None = None) -> bool:
-        try:
-            async with get_async_db_context(db) as db:
-                chat = await db.get(Chat, id)
-                chat.meta = {
-                    **chat.meta,
-                    'tags': [],
-                }
-                await db.commit()
-
-                return True
-        except Exception:
-            return False
-
     async def delete_chat_by_id(self, id: str, db: AsyncSession | None = None) -> bool:
         try:
             async with get_async_db_context(db) as db: