Sorry but this is a service we never offered and I see no reason why we should start. So far in our history, no posts have ever been deleted to free up space and what exists of the past, with a few isolated exceptions, is a perfect archive of everything that was said since ~2001.
I have no clue why anyone would want his/her account removed and all traces deleted so if the matter is of great importance to you, only your argumentation could convince me.