net: hns3: remove the useless debugfs file node cmd

mainline inclusion
from mainline-v5.14-rc1
commit b4689aaf
category: feature
bugzilla: NA
CVE: NA

----------------------------

Currently, all debugfs commands have been reconstructed, and the
debugfs file node cmd is useless. So remove this debugfs file node.

Signed-off-by: Yufeng Mo <moyufeng@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yonglong Liu <liuyonglong@huawei.com>
Reviewed-by: Junxin Chen <chenjunxin1@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>