GREG-411: Stop email to unaffiliated sponsors

When a sponsor is no longer affiliated with their institution as an employee, we still try to send them emails about roles ending. This causes a 550 SMTP error, because their work email no longer exists. When queuing role end notifications, we find which sponsor to send the emails to by checking which sponsors are connected to the role's OU. We can remove the OU from the unaffiliated sponsor, so we no longer send role end notifications to them.