[Frontend][Core] Revert "Add shutdown timeout" (#34730 and #36270) (#36628)

Signed-off-by: Mark McLoughlin <markmc@redhat.com>

vllm/config/vllm.py

@@ -327,12 +327,6 @@ class VllmConfig:
     weight_transfer_config: WeightTransferConfig | None = None
     """The configurations for weight transfer during RL training."""
 
-    shutdown_timeout: int = Field(default=0, ge=0)
-    """Shutdown grace period for in-flight requests. Shutdown will be delayed for
-    up to this amount of time to allow already-running requests to complete. Any
-    remaining requests are aborted once the timeout is reached.
-    """
-
     def compute_hash(self) -> str:
         """
         WARNING: Whenever a new field is added to this config,