Nothing used it meaningfully. Also, due to the way `init_prompt` was set
prior to b1401e2e4e, it would have been
very broken: the prompt_char would have been included in the line twice
and prompt substitutions like %T would have been cached. Even more,
trying to append the empty string to the prompt (removed in that commit)
caused us to add a number of workarounds removed in
1df442e0cf.
Adam Cammack
410eee8537