don't enable nav system always... that's not how this is supposed to work

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@11103 387891d4-d844-0410-90c0-e4c51a9137d3
well ok, revert that

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@11104 387891d4-d844-0410-90c0-e4c51a9137d3