Fix unused variable warnings
Fix unused variable warnings

Signed-off-by: Rudi Grinberg <4c46c202a3b8207ad5740134b125aae40c6c67a8@gmail.com>

samoht/ocaml-conduit,avsm/ocaml-conduit,mirage/ocaml-conduit,djs55/ocaml-conduit,djs55/ocaml-conduit,samoht/ocaml-conduit