The code paths for deleting a dossier were different, depending on
whether the dossier was deleted by the user, or from the Manager.
This commit unifies the two code paths into one.
This has the effect of:
- An operation log is now recorded when an user deletes its own dossier;
- Gestionnaires are now notified even when the dossier is deleted from
the Manager;
- The `support:delete_user_account` task now requires the email address
of the author.
