[V0 Deprecation] Deprecate --disable-frontend-multiprocessing (#37612)

Signed-off-by: sfeng33 <4florafeng@gmail.com>

vllm/entrypoints/openai/api_server.py

@@ -79,7 +79,6 @@ async def build_async_engine_client(
     args: Namespace,
     *,
     usage_context: UsageContext = UsageContext.OPENAI_API_SERVER,
-    disable_frontend_multiprocessing: bool | None = None,
     client_config: dict[str, Any] | None = None,
 ) -> AsyncIterator[EngineClient]:
     if os.getenv("VLLM_WORKER_MULTIPROC_METHOD") == "forkserver":
@@ -98,13 +97,9 @@ async def build_async_engine_client(
         engine_args._api_process_count = client_config.get("client_count", 1)
         engine_args._api_process_rank = client_config.get("client_index", 0)
 
-    if disable_frontend_multiprocessing is None:
-        disable_frontend_multiprocessing = bool(args.disable_frontend_multiprocessing)
-
     async with build_async_engine_client_from_engine_args(
         engine_args,
         usage_context=usage_context,
-        disable_frontend_multiprocessing=disable_frontend_multiprocessing,
         client_config=client_config,
     ) as engine:
         yield engine
@@ -115,7 +110,6 @@ async def build_async_engine_client_from_engine_args(
     engine_args: AsyncEngineArgs,
     *,
     usage_context: UsageContext = UsageContext.OPENAI_API_SERVER,
-    disable_frontend_multiprocessing: bool = False,
     client_config: dict[str, Any] | None = None,
 ) -> AsyncIterator[EngineClient]:
     """
@@ -129,9 +123,6 @@ async def build_async_engine_client_from_engine_args(
     # Create the EngineConfig (determines if we can use V1).
     vllm_config = engine_args.create_engine_config(usage_context=usage_context)
 
-    if disable_frontend_multiprocessing:
-        logger.warning("V1 is enabled, but got --disable-frontend-multiprocessing.")
-
     from vllm.v1.engine.async_llm import AsyncLLM
 
     async_llm: AsyncLLM | None = None