[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/torchair/torchair_sfa.py

@@ -21,8 +21,6 @@ from vllm_ascend.ascend_config import get_ascend_config
 from vllm_ascend.attention.attention_v1 import AscendAttentionState
 from vllm_ascend.attention.utils import (AscendCommonAttentionMetadata,
                                          split_decodes_and_prefills)
-from vllm_ascend.multistream.base import MSAttentionMetadataSplitConfig
-from vllm_ascend.multistream.ms_split import model_input_split_v1_mla_attn
 from vllm_ascend.torchair.utils import TorchairCommonAttentionMetadata
 from vllm_ascend.utils import is_enable_nz
 from vllm_ascend.worker.npu_input_batch import InputBatch
@@ -141,7 +139,6 @@ class AscendSFATorchairMetadata:
 
     decode: Optional[AscendSFATorchairDecodeMetadata] = None
     prefill: Optional[AscendSFATorchairPrefillMetadata] = None
-    enable_dbo_across_dp: bool = False
     is_prefill: bool = False
     is_decode: bool = False
 
@@ -154,17 +151,6 @@ class AscendSFATorchairMetadata:
         #         f"Only {supported_head_sizes} are supported for head_dim,",
         #         f"received {self.head_dim}.")
 
-    def split_metadata_for_multistream(
-        self,
-        ms_split_config: MSAttentionMetadataSplitConfig,
-    ) -> list["AscendSFATorchairMetadata"]:
-        """Split metadata for multi-stream with AscendSFATorchairMetadata"""
-        return model_input_split_v1_mla_attn(
-            ms_split_config=ms_split_config,
-            attn_metadata=self,
-            _metadata_cls=AscendSFATorchairMetadata,
-        )
-
 
 M = TypeVar("M", bound=AscendSFATorchairMetadata)
 
@@ -616,7 +602,6 @@ class AscendSFATorchairMetadataBuilder:
             query_start_loc=query_start_loc,
             block_tables=block_table,
             seq_lens=seq_lens,
-            enable_dbo_across_dp=common_attn_metadata.enable_dbo_across_dp,
             is_prefill=is_prefill,
             is_decode=is_decode)