[main] remove dbo code (#3712)

### What this PR does / why we need it?
Remove codes of dbo.
Currently, vLLM has supported dbo with pr:
https://github.com/vllm-project/vllm/pull/23693.

### Does this PR introduce _any_ user-facing change?

### How was this patch tested?

- vLLM version: v0.11.0rc3
- vLLM main:
17c540a993

Signed-off-by: zzzzwwjj <1183291235@qq.com>

vllm_ascend/attention/attention_v1.py

@@ -210,9 +210,6 @@ class AscendMetadata:
     # (num_tokens,)
     slot_mapping: torch.Tensor = None
 
-    # *************************** Other Properties *************************** #
-    enable_dbo_across_dp: bool = False
-
     prefill: Optional[AscendMetadataForPrefill] = None
 
     decode_meta: Optional[AscendMetadataForDecode] = None
@@ -371,7 +368,6 @@ class AscendAttentionMetadataBuilder:
             slot_mapping=slot_mapping,
             attn_mask=attn_mask,
             attn_state=attn_state,
-            enable_dbo_across_dp=common_attn_metadata.enable_dbo_across_dp,
             num_prefills=num_prefills,
             num_decodes=num_decodes,
             prefill=prefill_metadata,