This leads to multiple problems
1. We cant assume only items with id='current' are stored in the node
which would lead to retracting 'current' but another item would become
the last published and sent to users
2. Even if we have a SingletonNode retracting the only item means the Node
would be empty and offline clients would not receive the last published item
on coming online, because there is no item anymore
Instead we always publish an empty item from now on
- If the server implements XEP-0398 we dont need to add the avatar sha
anymore, the server adds it for us.
- It also means we dont have to query our own avatar from vcard at start
because the server tells us the avatar sha that is published with the inital
presence reflection
