Delete Account: Admin and User themselves Not Able to Delete Account

[mariobehling]

Trying to delete an account is not possible. Steps to reproduce:

1. User registers and buys a ticket
2. User order is canceled by organizer
3. User tries to delete account (without associated events or orders now) - not possible.
4. Admin tries to delete account in admin section - results in error message. Deletion is not possible.

Compare user account "Kathy Ho"
https://eventyay.com/admin/users/all?search=kathy