[V0 Deprecation] Remove VLLM_USE_V1 from tests (#26341)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/config/test_mp_reducer.py

@@ -8,16 +8,13 @@ from vllm.engine.arg_utils import AsyncEngineArgs
 from vllm.v1.engine.async_llm import AsyncLLM
 
 
-def test_mp_reducer(monkeypatch):
+def test_mp_reducer():
     """
     Test that _reduce_config reducer is registered when AsyncLLM is instantiated
     without transformers_modules. This is a regression test for
     https://github.com/vllm-project/vllm/pull/18640.
     """
 
-    # Use V1 AsyncLLM which calls maybe_register_config_serialize_by_value
-    monkeypatch.setenv("VLLM_USE_V1", "1")
-
     # Ensure transformers_modules is not in sys.modules
     if "transformers_modules" in sys.modules:
         del sys.modules["transformers_modules"]