[Frontend] merge beam search implementations (#9296)

vllm/entrypoints/openai/serving_completion.py

@@ -8,8 +8,6 @@ from typing import Tuple, Union, cast
 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.logger import RequestLogger
 # yapf conflicts with isort for this block
@@ -151,11 +149,6 @@ class OpenAIServingCompletion(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."
                     generator = self.engine_client.beam_search(
                         prompt_inputs["prompt_token_ids"],
                         request_id_item,