WP Symposium - 7th Pass update

* Remove 'Order By' from `_bbp_forum_id`
(This is already in place with `menu_order` on Line#77)
* Remove extra `join_tablename` from reply section
(We are limited here for now until we add support for more complex
joining in `converter.php`, for now leave the hardcoded table name in
the `from_expression` above)