[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/register_custom_ops.py

@@ -20,10 +20,9 @@ def _maybe_chunk_residual_impl(x: torch.Tensor,
         return residual
 
     if x.size(0) != residual.size(0):
-        flashcomm_v1_enabled = forward_context.flashcomm_v1_enabled
-        assert flashcomm_v1_enabled is True, (
-            "Currently, this situation only occurs "
-            "when flashcomm_v1 is enabled")
+        sp_enabled = forward_context.sp_enabled
+        assert sp_enabled is True, ("Currently, this situation only occurs "
+                                    "when sp is enabled")
         pad_size = forward_context.pad_size
         if pad_size > 0:
             residual = F.pad(residual, (0, 0, 0, pad_size))
@@ -41,8 +40,8 @@ def _maybe_all_gather_and_maybe_unpad_impl(x: torch.Tensor,
     except AssertionError:
         return x
 
-    flashcomm_v1_enabled = forward_context.flashcomm_v1_enabled
-    if flashcomm_v1_enabled and label:
+    sp_enabled = forward_context.sp_enabled
+    if sp_enabled and label:
         x = tensor_model_parallel_all_gather(x, 0)
         pad_size = forward_context.pad_size
         if pad_size > 0:
@@ -56,8 +55,8 @@ def _maybe_pad_and_reduce_impl(x: torch.Tensor) -> torch.Tensor:
     except AssertionError:
         return tensor_model_parallel_all_reduce(x)
 
-    flashcomm_v1_enabled = forward_context.flashcomm_v1_enabled
-    if flashcomm_v1_enabled:
+    sp_enabled = forward_context.sp_enabled
+    if sp_enabled:
         pad_size = forward_context.pad_size
         if pad_size > 0:
             x = F.pad(x, (0, 0, 0, pad_size))