net: hns3: remove some unused function hns3_update_promisc_mode()

hns3_update_promisc_mode is defined, but not be used, so remove it.

Signed-off-by: Guojia Liao <liaoguojia@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>