[Frontend] merge beam search implementations (#9296)

vllm/entrypoints/openai/serving_chat.py

@@ -9,8 +9,6 @@ from typing import Union
 from fastapi import Request
 
 from vllm.config import ModelConfig
-from vllm.engine.async_llm_engine import AsyncLLMEngine
-from vllm.engine.multiprocessing.client import MQLLMEngineClient
 from vllm.engine.protocol import EngineClient
 from vllm.entrypoints.chat_utils import (ConversationMessage,
                                          apply_hf_chat_template,
@@ -237,11 +235,6 @@ class OpenAIServingChat(OpenAIServing):
                 log_tracing_disabled_warning()
 
             if isinstance(sampling_params, BeamSearchParams):
-                assert isinstance(self.engine_client,
-                                    (AsyncLLMEngine,
-                                    MQLLMEngineClient)), \
-                    "Beam search is only supported with" \
-                    "AsyncLLMEngine and MQLLMEngineClient."
                 result_generator = self.engine_client.beam_search(
                     engine_inputs['prompt_token_ids'],
                     request_id,