[Refactor] [SP]The sequence parallelism characteristics in the MoE and Dense models are integrated into a single solution. (#3085)

What this PR does / why we need it?

there are two sets of sp implementations for moe and dense models. One
is called sequence_parallelism, and the other is flashcomm_v1.
We did the following things：

Merge two sets of code with the same implementation into one.
Remove the implementation of sequence_parallelism, as this solution
cannot support aclgraph.
Does this PR introduce any user-facing change?

No

How was this patch tested?

e2e&ut

- vLLM version: v0.10.2
- vLLM main:
f225ea7dd9

---------

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

vllm_ascend/attention/attention_v1.py

@@ -163,7 +163,6 @@ class AscendMetadata:
 
     # *************************** Other Properties *************************** #
     enable_dbo_across_dp: bool = False
-    is_only_prefill: bool = False
 
 
 class AscendAttentionMetadataBuilder:
@@ -236,8 +235,7 @@ 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,
-            is_only_prefill=common_attn_metadata.is_only_prefill)
+            enable_dbo_across_dp=common_attn_metadata.enable_dbo_across_dp)
         return attn_metadata
 
     def build_for_graph_capture(