The only thing using this AFAIK is dexctl in api_driver mode, which
no-one uses - it's a sort of weird API which requires a client to create
other clients, and gives all clients the ability to list all other
clients. So we are removing it.
This change solves the User's API problem when you want to create an user that its email hasn't been verified yet but it exist.
At now, you can resend invitation email using endpoint /users/{id}/resend-invitation
Fixes#184
