remove get_metadata_cls (#4087)

remove get_metadata_cls. It's only used for V0 engine and has been removed from vLLM already.

- vLLM version: v0.11.0
- vLLM main:
83f478bb19

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

tests/ut/attention/test_mla_v1.py

@@ -18,10 +18,6 @@ class TestAscendMLABackend(TestBase):
     def test_get_name(self):
         self.assertEqual(AscendMLABackend.get_name(), "ASCEND_MLA")
 
-    def test_get_metadata_cls(self):
-        self.assertEqual(AscendMLABackend.get_metadata_cls(),
-                         AscendMLAMetadata)
-
     def test_get_builder_cls(self):
         self.assertEqual(AscendMLABackend.get_builder_cls(),
                          AscendMLAMetadataBuilder)