Was previously supposed to be conditionally advertised based on
availability of a module handling the actual optimizations, which was
removed in be9ac41f1619
This was meant to warn in case you had only mod_csi without a logic
handling module like mod_csi_simple by checking if anything hooked this
event, however mod_smacks also hooks this event and so this isn't really
a useful way of detecting this condition.
This method ends up going up for each collection and the :clear() method
is only available to global modules (see e.g. mod_c2s), while regular
per-host modules get scoped stats
