bug#56885: Fix url-about.el in EWW or make it obsolete

[Stefan Kangas]

Severity: minor

Is url-about.el useful?  I note that evaluating this works:

    (pop-to-buffer (url-retrieve-synchronously "about:protocols"))

However, when I try to view that HTML in EWW like so, it does not work:

    M-x eww RET about:protocols RET

I just get a buffer saying "Loading http://about:protocols/...";, but not
the expected list of protocols.

I think this should either be fixed to work in EWW, or we should decide
that url-about.el is no longer useful and therefore mark it obsolete.