The /forums route is a default route for forums.
For example, this thread is in the XenForo Questions and Support forum:
http://xenforo.com/community/forums/xenforo-questions-and-support.25/
This thread however is in the threads route:
http://xenforo.com/community/threads/forum-is-in-root-but.74751/
Members have another route:
http://xenforo.com/community/members/tekgirl.13473/
All of those routes have a common element which in this case is /community, as that is where the software is installed.
In your case, you have installed in the root so there is no /community.
There will still be /forums, /threads, /members, etc. though.
You can change those using Route Filters, but you can't remove them as they are required for correct operation of the software.