Removing redundant python version check (vllm-project#20888)

Signed-off-by: Dannyso05 <dansong1177@gmail.com>

Author: Dannyso05

vllm/entrypoints/openai/serving_engine.py

@@ -18,11 +18,6 @@
 from starlette.datastructures import Headers
 from typing_extensions import TypeIs
 
-if sys.version_info >= (3, 12):
-    from typing import TypedDict
-else:
-    from typing_extensions import TypedDict
-
 if sys.version_info >= (3, 12):
     from typing import TypedDict
 else: