Sam.. go into PHPAdmin...go to

wp_wpforo_posts

and change the "modified" time to the same as "created" time

That will remove the "edited time on your forum

There is no an action buttons or settings. But you can hide it using a simple CSS code:

#wpforo #wpforo-wrap .wpforo-post .wpf-right .wpf-post-edited{display:none;}