[Misc] Fix import error in tensorizer tests and cleanup some code (#10349)

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

vllm/entrypoints/llm.py

@@ -964,6 +964,3 @@ class LLM:
         # This is necessary because some requests may be finished earlier than
         # its previous requests.
         return sorted(outputs, key=lambda x: int(x.request_id))
-
-    def _is_encoder_decoder_model(self):
-        return self.llm_engine.is_encoder_decoder_model()