[Perf] Delete redundant operations in model_runner and forward_context (#3677)

### What this PR does / why we need it?

Remove redundant operations from `model_runner` and `forward_context`.
This optimization can significantly reduce the idle time (bubble) before
decoding when running models with small parameter counts (e.g.,
Qwen/Qwen2.5-0.5B).

Testing on 800I A2, bubble is reduced from 3.8ms to 2.8ms :
Before
<img width="1655" height="696" alt="image"
src="https://github.com/user-attachments/assets/d7608e52-2438-46dd-8fc9-391fd6274495"
/>

After
<img width="1607" height="774" alt="image"
src="https://github.com/user-attachments/assets/56daf081-2dba-4d2e-99d4-e055187d9806"
/>

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?


- vLLM version: v0.11.0rc3
- vLLM main:
https://github.com/vllm-project/vllm/commit/releases/v0.11.1

---------

Signed-off-by: realliujiaxu <realliujiaxu@163.com>

vllm_ascend/ops/fused_moe/moe_comm_method.py

@@ -37,7 +37,7 @@ _MoECommMethods: Dict[Optional[MoECommType], MoECommMethod] = {}
 
 def get_moe_comm_method(
         moe_comm_type: Optional[MoECommType]) -> Optional[MoECommMethod]:
-    return _MoECommMethods.get(moe_comm_type)
+    return _MoECommMethods.get(moe_comm_type, None)
 
 
 def setup_moe_comm_method(moe_config):