Remove ghost feature: api.HTMLAreaElement.hreflang

[queengooborg]

A number of my recent PRs have been setting api.HTMLAreaElement.hreflang to false. It has been determined that this feature is actually a ghost feature, with no implementation or spec. This feature should be removed from BCD.

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There’s no HTMLAreaElement.prototype.hreflang in Blink or Gecko either — and https://html.spec.whatwg.org/multipage/image-maps.html#htmlareaelement doesn’t actually define a hreflang member for HTMLAreaElement, not even as an obsolete member in https://html.spec.whatwg.org/multipage/obsolete.html#HTMLAreaElement-partiall. And there is actually no https://developer.mozilla.org/en-US/docs/Web/API/HTMLAreaElement/hreflang article.

So it seems to me we should just remove this entire feature.

Originally posted by @sideshowbarker in #7402 (comment)

[queengooborg]

Resolved by #7539.