[Refactor] remove some metadata variables in attention_v1. (#5160)

RFC: https://github.com/vllm-project/vllm-ascend/issues/4629

Reason:

The metadata data class contains an excessive number of variables. We
will inherit the metadata of the community and simultaneously remove
some variables that are no longer needed at present.

Todo:
1. remove attn_state partly.

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: weijinqian_v1 <weijinqian@huawei.com>
Co-authored-by: weijinqian_v1 <weijinqian@huawei.com>

vllm_ascend/attention/mla_v1.py

@@ -23,6 +23,7 @@ from vllm_ascend import envs
 from vllm_ascend.ascend_config import get_ascend_config
 from vllm_ascend.attention.attention_v1 import AscendAttentionState
 from vllm_ascend.attention.utils import (AscendCommonAttentionMetadata,
+                                         enable_cp,
                                          maybe_save_kv_layer_to_connector,
                                          split_decodes_and_prefills,
                                          trans_rope_weight, transdata,
@@ -57,8 +58,7 @@ class AscendMLABackend(AttentionBackend):
 
     @staticmethod
     def get_builder_cls():
-        prefill_config = get_current_vllm_config().parallel_config
-        if prefill_config.prefill_context_parallel_size > 1 or prefill_config.decode_context_parallel_size > 1:
+        if enable_cp():
             from vllm_ascend.attention.mla_cp import AscendMlaCPMetadataBuilder
             return AscendMlaCPMetadataBuilder
         return AscendMLAMetadataBuilder
@@ -70,8 +70,7 @@ class AscendMLABackend(AttentionBackend):
 
     @staticmethod
     def get_impl_cls() -> Type["MLAAttentionImpl"]:
-        prefill_config = get_current_vllm_config().parallel_config
-        if prefill_config.prefill_context_parallel_size > 1 or prefill_config.decode_context_parallel_size > 1:
+        if enable_cp():
             from vllm_ascend.attention.mla_cp import AscendMlaCPImpl
             return AscendMlaCPImpl
         return AscendMLAImpl