Stop passing CRM_Core_DAO::$_nullArray pointlessly

Probably a bit of an ongoing on but it turns out that

CRM_Core_DAO::$_nullArray

is just a static var and it isn't always NULL!

so a line like this

CRM_Core_DAO::executeQuery($query, CRM_Core_DAO::$_nullArray);

can potentially pick up parameters from the last time the static was used.

Fortunately very few of the instances it is being used in still require it!