If you're getting this error then your server doesn't have PHP 5.3 or higher installed (or it is not using it) and thus does not meet the minimum requirements to run VaultWiki. You will have to upgrade to a newer version of PHP or not use VaultWiki. I should note that the makers of PHP do not even support 5.3 anymore because it's already that old.
Still, this error was related to unused code and has been removed for the next release. Marking as fixed.