I too was having this problem (I am an administrator in the system). The problem lies in which view pane you are in while trying to delete the section. If you are trying to delete from the right pane view (usually titled 'Sections and Cases,' there is no way to delete.
Adjacent to the 'Add Section' button in the right pane there is a drop-down dialog with three view options, 'All groups and tests', 'Selected group and subgroups', and 'Selected group only'. In my install, the default is 'Selected group and subgroups'. Change to the 'All groups and tests' view and the section will now show up in the left (main) view. Now mouse over your section name and the delete icon (red circle with a '-' character) that Tobias from Gurock mentions. Click the delete icon and the unwanted section will be removed.