builtin/prune: convert to struct object_id

Convert the sole instance of unsigned char [20] to struct object_id.
cmd_prune is a caller of parse_object, which we will convert later.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/prune.c

@@ -123,11 +123,11 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 		die(_("cannot prune in a precious-objects repo"));
 
 	while (argc--) {
-		unsigned char sha1[20];
+		struct object_id oid;
 		const char *name = *argv++;
 
-		if (!get_sha1(name, sha1)) {
-			struct object *object = parse_object_or_die(sha1, name);
+		if (!get_oid(name, &oid)) {
+			struct object *object = parse_object_or_die(oid.hash, name);
 			add_pending_object(&revs, object, "");
 		}
 		else