Raised when a user is deleted from all user directories visible to the server.
Clients that store data used to authenticate or authorize a user should subscribe to this event to
clean up data related to the deleted user. For example, if a plugin stores a secure key used to authenticate a user,
it should listen for this event and delete those keys. Note that content created by the user typically shouldn't be
deleted when the user is deleted, as it may still be of historical interest.
This event is raised for every deleted user.