security: drop the unused hook skb_owned_by

The skb_owned_by hook was added with the commit ca10b9e9a8ca
("selinux: add a skb_owned_by() hook") and later removed
when said commit was reverted.

Later on, when switching to list of hooks, a field named
'skb_owned_by' was included into the security_hook_head struct,
but without any users nor caller.

This commit removes the said left-over field.

Fixes: b1d9e6b0646d ("LSM: Switch to lists of hooks")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: Paul Moore <pmoore@paul-moore.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>

include/linux/lsm_hooks.h

@@ -1804,7 +1804,6 @@ struct security_hook_heads {
 	struct list_head tun_dev_attach_queue;
 	struct list_head tun_dev_attach;
 	struct list_head tun_dev_open;
-	struct list_head skb_owned_by;
 #endif	/* CONFIG_SECURITY_NETWORK */
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
 	struct list_head xfrm_policy_alloc_security;

security/security.c

@@ -1848,7 +1848,6 @@ struct security_hook_heads security_hook_heads = {
 	.tun_dev_attach =
 		LIST_HEAD_INIT(security_hook_heads.tun_dev_attach),
 	.tun_dev_open =	LIST_HEAD_INIT(security_hook_heads.tun_dev_open),
-	.skb_owned_by =	LIST_HEAD_INIT(security_hook_heads.skb_owned_by),
 #endif	/* CONFIG_SECURITY_NETWORK */
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
 	.xfrm_policy_alloc_security =