Deleted event instances should redirect to their series page

Problem/Motivation

People may keep track of links to events they are interested in. If an event instance is deleted, they just see a generic page not found page. Same for search engines.

Steps to reproduce

1. Create an event series with multiple events
2. Visit an individual instance and copy the url for that page
3. Delete the event instance
4. Visit the url of the deleted instance
5. See page not found page

Proposed resolution

Deleted event instances should just redirect to the event series page that they were created from. I think this might require integration with the redirect module. Maybe this logic could only be performed if the module is installed, rather than depending on it.