Delete this account
I'm afraid, in any MediaWiki sites, delete an account is not (at least, at this moment) be possible, see discussion in phab:T34815.
Maybe, we should rename you as User:Vanished~something?
As can be seen here, my account was rejected and created afterwards (meaning it was completely deleted when it was rejected at first). I knew that MediaWiki doesn't allow this, but the fact that my account was deleted resulted in my impression that deletion is indeed possible (and as it seems it really is, but from your answer I take that this is not when the account was accepted once. Closing this issue is correct then, just leave it as it is.