[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/ops/common_fused_moe.py

@@ -216,7 +216,9 @@ class AscendFusedMoE(FusedMoE):
 
         forward_context = get_forward_context()
         hidden_states, router_logits = forward_context.moe_comm_method.prepare(
-            hidden_states=hidden_states, router_logits=router_logits)
+            hidden_states=hidden_states,
+            router_logits=router_logits,
+            replace_allreduce=forward_context.sp_enabled)
 
         # Matrix multiply.
         final_hidden_states = self.quant_method.apply(