We were using a `height: $line-height` property for this task. One of
the disadvantages of this approach is that things don't look so great
when the label expands over more than one line.
Back when we added that property, browser support for flex layouts
wasn't that great. Now there's universal support for it, so we can use
it instead.
This way changing it will be easier.
Note we're moving the `legislation-draft-versions-form` class into the
form component itself, which is wat we usually do in components.
