Fix some issues in API (#2902)

### What problem does this PR solve?

Fix some issues in API

### Type of change

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

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

sdk/python/ragflow/modules/chat.py

@@ -73,6 +73,3 @@ class Chat(Base):
         res = res.json()
         if res.get("code") != 0:
             raise Exception(res.get("message"))
-
-    def get_prologue(self):
-        return self.prompt.opener