tty: Deprecate no-regfile entry case

TTY files carry link on regfile entry since 1.4 (commit caa64d97)
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>

criu/tty.c

@@ -1541,6 +1541,9 @@ static int collect_one_tty(void *obj, ProtobufCMessage *msg, struct cr_img *i)
 	 */
 	info->reg_d = try_collect_special_file(info->tfe->id, 1);
 	if (!info->reg_d) {
+		if (!deprecated_ok("TTY w/o regfile"))
+			return -1;
+
 		if (is_pty(info->driver)) {
 			info->reg_d = pty_alloc_reg(info, true);
 			if (!info->reg_d) {