The forum is not part of your site it is a free standing service on a different server intended to be used on any site with any web host. Just because you sign up for both the forum and web hosting in the same Bravenet account there is no assumption that you want to use them together.
Bravenet's Website Wizard automatically builds the NavBar on the basis of what pages you create on your site. If you don't want the NavBar designed in that way then the answer is to stop using the Wizard and to use Bravenet's Visual Editor or one of the hundreds of third party web page editors on the market.