EntityPerPage::getEntitiesWithoutSitelinks should move into a separate EntityWithoutSitelinksFinder, and should be re-implemented based on the page and page_props table instead of entity_per_page. Implementations should use page_props to find items without sitelinks instead of joining against wb_items_per_site.
NOTE: This function is only needed for Special:EntitiesWithoutSitelinks. We should evaluate how much need there is for this functionality before blocking on it, or investigating a lot of time.