Summary:
Ref T10747. If you accidentally import the wrong thing, you can clean up the big mess you made.
These imported events are read-only so it's OK to destroy them completely (vs disable/hide/archive).
Test Plan: Destroyed some imported events.
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10747
Differential Revision: https://secure.phabricator.com/D16720
