selftests: bonding: remove redundant delete action of device link1_1

When run command "ip netns delete client", device link1_1 has been
deleted. So, it is no need to delete link1_1 again. Remove it.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>