netlabel: Remove unused declaration netlbl_cipsov4_doi_free()

Since commit b1edeb10 ("netlabel: Replace protocol/NetLabel linking with refrerence counts")
this declaration is unused and can be removed.

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Link: https://lore.kernel.org/r/20230801143453.24452-1-yuehaibing@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>