Reconsider the impact of the parent/child rules

With axe-core support for IE deprecated, it is no longer quite as important for pages to get their parent/child relationships correct. One case that came up recently was where a site had double-nested their dd / dt elements in divs:

```html

Hello world

This fails axe-core. However the importance of this to screen readers seems pretty minimal. Where this may still matter is to people who make heavy use of custom style sheets. If you wanted an alternative presentation of definition lists you may use `dl:has(> dt, > dd, > div > dt, > div > dd)` as a selector. This would let you style valid definition lists, but it would break on this invalid scenario.

Since custom style sheets are often highly individualized there isn't a big repository out there we could check to see if this is an issue. It still theoretically could be, but it is difficult to know whether in practice this creates accessibility issues. We should do some research in this subject and figure out whether impact needs to be updated and/or maybe this should no longer fail under WCAG.

There are quite a few rules that do parent/child relationship checking. We'll probably need to update them all for this.

- list
- listitem
- definition-list
- dlitem
- aria-required-child
- aria-required-parent