[Refactor] Implement output type check in LLM (#34794)

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

vllm/v1/engine/llm_engine.py

@@ -199,10 +199,6 @@ class LLMEngine:
             self.should_execute_dummy_batch = True
         return aggregated_has_unfinished
 
-    @classmethod
-    def validate_outputs(cls, outputs, output_type):
-        return outputs
-
     def get_supported_tasks(self) -> tuple[SupportedTask, ...]:
         if not hasattr(self, "_supported_tasks"):
             # Cache the result