[V1][Platform] Remove supports_structured_output() in platform (#531)

### What this PR does / why we need it?
Remove `supports_structured_output()` in platform. This method is no need, because upstream has deleted this.

Signed-off-by: shen-shanshan <467638484@qq.com>

Author: shen-shanshan

vllm_ascend/platform.py

@@ -162,7 +162,3 @@ def supports_v1(cls, model_config: ModelConfig) -> bool:
         model configuration.
         """
         return True
-
-    @classmethod
-    def supports_structured_output(cls) -> bool:
-        return True