Issue #3315836 by owenbush, nifsight: Deleting old events with registrants

...registration/recurring_events_registration.links.menu.yml

..._events_registration/recurring_events_registration.module

...ts_registration/recurring_events_registration.routing.yml

...s/recurring_events_registration/src/Entity/Registrant.php

...ts_registration/src/Form/OrphanedEventRegistrantsForm.php

recurring_events.links.menu.yml

recurring_events.permissions.yml

recurring_events.routing.yml

src/Form/OrphanedEventInstanceForm.php