DeleteOwnIdentityPage: Use ErrorPage instead of duplicating its code
DeleteOwnIdentityPage: Remove obsolete TODO
- This TODO was from a time when the MyIdentityPage displayed all OwnIdentitys. Nowadays, that page is only accessible when being logged in as a certain identity, and then only displays that identity. So it doesn't make any sense to display it after having deleted an identity because there would be nothing to display. The existing approach of inlining the log-in page is fine.