SessionHandler: Remove version check for PHP >= 5.2 when calling setcookie.

Since 5.2.0 is now the minimum supported version, this check is no longer
necessary.

Thanks to Ryan Panning for providing this patch.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@3060 44740490-163a-0410-bde0-09ae8108e29a