Remove `status` and `traceback` from completion response on the server

[Yi Xu]

We removed this from our internal version (we'll be moving to public repo-first development soon!), we just need to remove from the public repo too:

llm-engine/server/llm_engine_server/common/dtos/llms.py

Lines 117 to 119 in b2588ea

 status: TaskStatus 
 outputs: List[CompletionOutput] 
 traceback: Optional[str] = None 

[Sai Atmakuri]

Done as part of #214