Plugin don't delete their settings after uninstall

Plugin don’t delete their settings after uninstall. Can you solve this problem?

I add uninstall.php file into the plugin folder with such content:

<?php
if( ! defined('WP_UNINSTALL_PLUGIN') )
	exit;

delete_option('slb_options');
delete_option('slb_version');

Is it normal?
Why plugin don’t have such file?