Want to remove the nagging update notice from your WordPress site? Sometimes this can be helpful if you built the site for someone else and don’t want them upgrading it. Perhaps there are plugins running on the site that won’t be compatible with the update. Here’s a quick snippet to remove the notice from your site:
add_filter( 'pre_site_transient_update_core', create_function( '$a', "return null;" ) );
Simply add that to your functions.php file and click save and the notices will disappear.