[main] adapt usage of npu_moe_gating_top_k_softmax and remove envs.SELECT_GATING_TOPK_SOTFMAX_EXPERTS (#2112)

backport of v0.9.1-dev:
https://github.com/vllm-project/vllm-ascend/pull/1902

origin main npu_moe_gating_top_k_softmax:
https://github.com/vllm-project/vllm-ascend/pull/1355

- vLLM version: v0.10.0
- vLLM main:
055bd3978e

Signed-off-by: huangxialu <huangxialu1@huawei.com>

vllm_ascend/envs.py

@@ -117,11 +117,6 @@ env_variables: Dict[str, Callable[[], Any]] = {
     # value to False to disable the optimized model.
     "USE_OPTIMIZED_MODEL":
     lambda: bool(int(os.getenv('USE_OPTIMIZED_MODEL', '1'))),
-    # SELECT_GATING_TOPK_SOTFMAX_EXPERTS is the equivalent of select_experts in non-quantized scenarios.
-    # In theory, it should have better performance than select_experts.
-    # Subsequent versions will remove the SELECT_GATING_TOPK_SOTFMAX_EXPERTS tag and use it as the default mode.
-    "SELECT_GATING_TOPK_SOTFMAX_EXPERTS":
-    lambda: bool(int(os.getenv("SELECT_GATING_TOPK_SOTFMAX_EXPERTS", '0'))),
     # The tolerance of the kv cache size, if the difference between the
     # actual kv cache size and the cached kv cache size is less than this value,
     # then the cached kv cache size will be used.