mark unused read_tree_recursive() callback parameters

We pass a callback to read_tree_recursive(), but not every callback
needs every parameter. Let's mark the unused ones to satisfy
-Wunused-parameter.

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

archive.c

@@ -382,7 +382,8 @@ struct path_exists_context {
 	struct archiver_args *args;
 };
 
-static int reject_entry(const struct object_id *oid, struct strbuf *base,
+static int reject_entry(const struct object_id *UNUSED(oid),
+			struct strbuf *base,
 			const char *filename, unsigned mode,
 			void *context)
 {