Deleting user from Unsynced from Directory causes Team Calendar to send out emails for all events the user was in

Issue Summary

1. Unsynced from Directory functionality was added in Confluence 6.13 due to GDPR requirements, where we can remove all details of a user who is no longer in Confluence and anonymize their names.
2. This also removes them from the Who section of events in team calendar, which in turn spams all users who are watching these calendars.
3. The longer a user has been using team calendar\more events, the more emails get sent out when they are removed via the Unsync.

Steps to Reproduce

1. Sync a user from an external directory to Confluence, and add them as participants in some events.
2. Remove them from the external directory and sync it to Confluence.
3. The user will now be in the Unsynced from Directory tab in the user management page.
4. Delete the user from here.
5. Any user who is watching the calendar that the event is in will receive an email for each event that the user was in.

Expected Results

1. No email should be sent for the removal of the user from these events.

Actual Results

1. Each event that the user was in would trigger an email to watchers of the calendar.

Workaround

1. Currently there is no known workaround for this behavior. A workaround will be added here when available