The URL spec recently changed and the variour "mixins" interfaces are gone,
this commit updates our code and WPT accordingly.
The new expected failures related to HTMLAnchorElement and HTMLAreaElement's
attributes are due to their moving to the HTMLHyperLinkElementUtils interface,
which is not anymore in a separate `<script class=untested>` element.
Source-Repo: https://github.com/servo/servo
Source-Revision: f73cd40282ab79f53b38f2b057677b0423282f32
