Toolbar tray shows stray border at narrow widths

In the attached screen shot, the right borders on Structure, People, and Configuration, are smart enough to go away because they are at the ends of lines, but Help stubbornly keeps its border. It looks really weird when the window is narrow enough that the menu is a single column (and the user is stubborn enough not to switch to vertical mode).

These are the lines of CSS at fault:

.toolbar .horizontal .menu li:last-child {
  border-right: 1px solid #dddddd; /* LTR */
}

(toolbar/css/toolbar.theme.css). I assume there are corresponding lines in toolbar.theme-rtl.css.

Can we just get rid of that right border? The toggle switch already has a left border.

Related issue

#1852348: Toggle to change orientation of toolbar is not easily discoverable.