[MISC] Clean up torch_npu (#688)

torch_npu 2.5.1 support autoload now. This patch does:
1. remove useless torch_npu import
2. replace `torch_npu.npu` to `torch.npu`.

Signed-off-by: wangxiyuan <wangxiyuan1007@gmail.com>

tests/singlecard/test_pyhccl.py

@@ -17,7 +17,6 @@
 # limitations under the License.
 #
 import torch
-import torch_npu  # noqa: F401
 
 from vllm_ascend.distributed.device_communicators.pyhccl_wrapper import \
     HCCLLibrary