[Bugfix][MoE] Remove All2All in w4a8_dynamic (#4977)

### What this PR does / why we need it?
GatherEP has been fixed in
https://github.com/vllm-project/vllm-ascend/pull/3279, remove all2all in
w4a8_dynamic scenario.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
e2e & ut
- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

Signed-off-by: weichen <calvin_zhu0210@outlook.com>

vllm_ascend/ascend_forward_context.py

@@ -248,10 +248,6 @@ def select_moe_comm_method(num_tokens: int,
                 and vllm_config.parallel_config.world_size_across_dp /
                 vllm_config.parallel_config.pipeline_parallel_size >= 16):
             moe_comm_type = MoECommType.MC2
-        else:
-            # Currently, w4a8_dynamic does not support allgatherep
-            if quant_type == "w4a8_dynamic":
-                moe_comm_type = MoECommType.ALLTOALL
         else:
             moe_comm_type = MoECommType.ALLGATHER