Switch back to official CSSWG specs

[Loirooriol]

What is the issue with the HTML Standard?

#8699 changed a bunch of drafts.csswg.org links into w3c.github.io, because the former server was frequently down.

This was later addressed, now drafts.csswg.org serves specs using Github pages.

w3c.github.io is not the official domain, so there is some JS that redirects users into drafts.csswg.org.

This is not much convenient, HTML should point to the official drafts.csswg.org directly.

[Loirooriol]

An example is https://html.spec.whatwg.org/multipage/webappapis.html#update-the-rendering, substep 14, it has some links to https://w3c.github.io/csswg-drafts/resize-observer-1/