Remove unused row_idx in token_dispatcher (#3442)

### What this PR does / why we need it?
The `row_idx` parameter is no longer used since
PR[#2689](https://github.com/vllm-project/vllm-ascend/pull/2689), so
remove it across multiple files to remove unnecessary calculations and
parameter passing.

### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
accuracy test passed for Qwen3 235B and DeepSeek V3 671B after this PR.


- vLLM version: v0.11.0rc3
- vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.0

---------

Signed-off-by: CaranLic <740821011@qq.com>

tests/ut/ops/test_fused_ops.py

@@ -263,7 +263,7 @@ class TestExpertsSelector:
 
         x = torch.randn(8, 2)
         router_logits = torch.randn(8, 2)
-        topk_weights, topk_ids, _ = select_experts(
+        topk_weights, topk_ids = select_experts(
             hidden_states=x,
             router_logits=router_logits,
             top_k=2,