Do not disable axe rules for definition lists

We wrap each name-value group in the summary list's `<dl>` with a grouping `<div>` element, which is valid according to the current WHATWG HTML spec [1].

At the time we wrote these tests, this was a relatively recent change to the HTML spec, and the axe rules had not been updated to allow it.

Since then, the underlying axe rules have been updated to allow wrapping `<div>` elements [2], so we no longer need to disable the `dlitem` and `definition-list` (released in axe-core 3.2.0 [3])

[1]: https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element
[2]: dequelabs/axe-core#1284
[3]: https://github.com/dequelabs/axe-core/blob/develop/CHANGELOG.md#320-2019-03-04

src/govuk/components/summary-list/template.test.js

@@ -14,14 +14,7 @@ describe('Summary list', () => {
  it('passes accessibility tests', async () => {
  const $ = render('summary-list', examples.default)
 
- const results = await axe($.html(), {
- rules: {
- // In newer versions of the HTML specification wrapper
- // <div>s are allowed in a definition list
- dlitem: { enabled: false },
- 'definition-list': { enabled: false }
- }
- })
+ const results = await axe($.html())
  expect(results).toHaveNoViolations()
  })
  })