Since the forum was moved to it’s current domain in august 2011, and the procedure to delete an account was depicted in September 2011 as requiring the Admin (se quote below), I doubt it has ever actually been an option for the user to self-delete his account, at least under the current domain.
- Delete all of your posts you want deleted
- PM me with the name you want your remaining posts credited under
Sidenote - Fun historical quote concerning what used to happen to spammer accounts:
There was one purge of inactive accounts a long time ago, and it used to be policy to delete the accounts of spammers. But accounts are almost never deleted nowadays.
Account self-deletion is feasable in SMF (see the three "this one" hyperlinks in the quoted text above), it’s probably just not there for Bitcointalk as a deliberate omission.