remove unused sitnl.h file

remove unused sitnl.h file

sitnl.h must have slipped in when implementing the networking AI and the
SITNL backend. However it is unused and should simply be removed.

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Lev Stipakov <lstipakov@gmail.com>
Message-Id: <20220314162048.22955-1-a@unstable.cc>
URL: https://www.mail-archive.com/search?l=mid&q=20220314162048.22955-1-a@unstable.cc
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit c697febbc2f445981a6042bb8deb9ed49beb5b73)