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

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

tests/v1/entrypoints/openai/test_completion.py

@@ -26,19 +26,12 @@ def default_server_args():
         "128",
         "--enforce-eager",
         "--enable-prompt-tokens-details",
+        "--no-enable-prefix-caching",
     ]
 
 
-@pytest.fixture(
-    scope="module",
-    params=[
-        ["--no-enable-prefix-caching"],
-        ["--no-enable-prefix-caching", "--disable-frontend-multiprocessing"],
-    ],
-)
-def server(default_server_args, request):
-    if request.param:
-        default_server_args = default_server_args + request.param
+@pytest.fixture(scope="module")
+def server(default_server_args):
     with RemoteOpenAIServer(MODEL_NAME, default_server_args) as remote_server:
         yield remote_server