rm key set in xinference (#2511)

### What problem does this PR solve?

#2492

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

rag/llm/chat_model.py

@@ -103,7 +103,6 @@ class XinferenceChat(Base):
             raise ValueError("Local llm url cannot be None")
         if base_url.split("/")[-1] != "v1":
             base_url = os.path.join(base_url, "v1")
-        key = "xxx"
         super().__init__(key, model_name, base_url)