The split() function has deprecated as of PHP 5.3.0. If you need the warning not to pop up you can change the PHP version to 5.2. If you need PHP 5.3 you can set error reporting lower in your php.ini file (errorfunc.configuration.php#ini.error-reporting).
To Change Your PHP Version
From the Content menu, select Programming Languages.
Select the PHP version you want to use, and then click Continue.
The deprecated warning indicates that PHP's developers may not continue to support the function. The preg_split() or str_split() functions are now the preferred alternatives to split().