[Bugfix] Remove cuda related lines and add additional pip mirror (#1252)

### What this PR does / why we need it?
- For npu environment, we should use `PYTORCH_NPU_ALLOC_CONF ` rather
than `PYTORCH_CUDA_ALLOC_CONF`
- Add `PIP_EXTRA_INDEX_URL` to make nightly_benchmarks happy


---------

Signed-off-by: wangli <wangli858794774@gmail.com>

.github/workflows/nightly_benchmarks.yaml

@@ -167,6 +167,8 @@ jobs:
           cp -r benchmarks/* /github/home/benchmarks/
 
       - name: Run benchmark iteration
+        env:
+          PIP_EXTRA_INDEX_URL: https://mirrors.huaweicloud.com/ascend/repos/pypi
         if: github.event_name != 'pull_request'
         run: |
           while IFS= read -r line || [[ -n "$line" ]]; do

vllm_ascend/device_allocator/camem.py

@@ -144,7 +144,7 @@ class CaMemAllocator:
         return CaMemAllocator.instance
 
     def __init__(self):
-        conf = os.environ.get("PYTORCH_CUDA_ALLOC_CONF", "")
+        conf = os.environ.get("PYTORCH_NPU_ALLOC_CONF", "")
         assert "expandable_segments:True" not in conf, \
             ("Expandable segments are not compatible with memory pool. "
             "Please track https://github.com/pytorch/pytorch/issues/147851 "