Remove document-domain policy-controlled feature.

[otherdaniel]

This adds a "Retired Features" section and moves document-domain there, as this appears to be the first feature to be removed.

The change is meant to support removal of the document-domain policy in HTML and Chromium.

• https://github.com/whatwg/html/pull/8549
• https://crrev.com/c/3930823

[clelland]

This looks good -- do you want to wait until whatwg/html#8549 lands, or do you think this should land first?

[otherdaniel]

This looks good -- do you want to wait until whatwg/html#8549 lands, or do you think this should land first?

Not sure. But since this claims that "their specification and/or implementations have been removed", it would seem more logical to wait for the HTML spec removal to land. :)

[otherdaniel]

[...] do you want to wait until whatwg/html#8549 lands [...]

That'd be now. :) Let's land this.

[clelland]

Done!