Allow disabling "question is question is answered; right answer is accepted" close reason — and consider just removing it

[mattdm]

Rationale: this isn't meant to be just a forum, where we have transient diagnostic threads. It's meant to build up a database of helpful answers. "Closed: this situation is not reproducible" might make sense, but we shouldn't be closing questions with solutions — we should be enshrining them.

And even then, there's always room for improvement — later answers even after one is accepted could elaborate with more detail, be update for newer approaches, or simply be better than the quick fix someone suggested first.

I'd suggest that there is almost never a reason to have this.