This list will display (up to) the first six additional leagues you are logged in to.  If you are currently logged into more than six additional leagues, the All My Leagues option will appear farther down in this menu.  Use this option to access your other leagues.  If you see a league listed there that you would no longer like listed, simply go to that league, and log out of that league, and you'll no longer see that league listed under the "My Leagues" menu item.