net: hns3: Remove unused struct member and definition

The struct hclge_desc_cb and hclge_desc_cb are never used in
anywhere. This patch removes them.

Signed-off-by: Jian Shen <shenjian15@huawei.com>
Signed-off-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>