It was only used once, and we can use a selector that makes it obvious
where it is used. Besides, the style for the no-margin-bottom class was
to remove the bottom margin, which was inconsistent with the style for
the no-margin-top class, which adds a negative margin to the element.
I'm not sure why we're removing the margin here, though, since it isn't
consistent with the rest of the forms in the application. For now, we're
keeping it the way it used to look.
