This SQL exists from first versions of wpForo. It just returns the number of posts for statistic purpose. In any case, if you want to test it, you can open the /wp-content/plugins/wpforo/wpf-includes/class-posts.php file, find this line:
$sql = "SELECT SQL_NO_CACHE COUNT(*) FROM `".WPF()->tables->posts."`";
and change it to this:
$sql = "SELECT COUNT(*) FROM `".WPF()->tables->posts."`";
In case you want to say thank you !) We'd really appreciate and be thankful if you leave a good review on plugin page. This is the best way to say thank you to this project and support team.