refs: mark unused each_ref_fn parameters

Functions used with for_each_ref(), etc, need to conform to the
each_ref_fn interface. But most of them don't need every parameter;
let's annotate the unused ones to quiet -Wunused-parameter.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -135,7 +135,8 @@ static int ref_filter_match(const char *refname,
 }
 
 static int add_ref_decoration(const char *refname, const struct object_id *oid,
-			      int flags, void *cb_data)
+			      int UNUSED(flags),
+			      void *cb_data)
 {
 	struct object *obj;
 	enum object_type objtype;