The skb_owned_by hook was added with the commit ca10b9e9
("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: b1d9e6b0 ("LSM: Switch to lists of hooks")
Signed-off-by: NPaolo Abeni <pabeni@redhat.com>
Acked-by: NCasey Schaufler <casey@schaufler-ca.com>
Acked-by: NPaul Moore <pmoore@paul-moore.com>
Signed-off-by: NJames Morris <james.l.morris@oracle.com>