If one has an account on any of the SE sites (Stack Overflow, Super User etc.), in order to delete their account, they can do so from their profile page. Numerous similar questions have been asked and answerers are always directed to this page:
However, even after one has deleted all their accounts and one is not a participant of any of the communities, one continues to be logged in when they visit www.stackexchange.com. Now, if one clicks on any of the communities (Stack Overflow, Meta etc.), they are first asked to join. But how does one delete their master account, so that instead of being asked to join, they are first asked to log in?