Here are the instructions for uninstalling multi-site on WordPress 3.0+:
Remove the constants from the wp-config.php file.
define (‘MULTISITE’, ‘1’);
define (‘SUBDOMAIN_INSTALL’, false);
define (‘DOMAIN_CURRENT_SITE’, ‘localhost’);
define (‘PATH_CURRENT_SITE’, ‘/wp-multi/’);
define (‘SITE_ID_CURRENT_SITE’, 1);
define (‘BLOG_ID_CURRENT_SITE’, 1);
$base = ‘/wp-multi/’;
Delete the htaccess and let WP create a fresh single-site one.
You can have it create a new one by simply going to your permalink settings page and click save again.
Remove the extra tables from the database. (The “wp_” will be replaced with whichever prefix you made during installation”)
wp_blogs
wp_blog_versions
wp_registration_log
wp_signups
wp_site
wp_sitemeta
Remove the two extra fields added to the users table.
spam
deleted
That should remove WordPress Multisite from your install.
Also, make sure you have deleted the browser cache as that might show the old data.