Modernize user and repository "delete" workflows and improve documentation
- The inability to destroy objects from the web UI is intentional. Make this clear in the messaging, which is somewhat out of date and partly reflects an earlier era when things could be destroyed.
- bin/remove destroy can't rewind time. Document expectations around the "put the cat back in the bag" use case.
Test Plan: Read documentation, clicked through both workflows.
Differential Revision: https://secure.phabricator.com/D20694