RFR: 8247957: remove doclint support for HTML 4

[Yoshiki Sato]

On Fri, 13 Nov 2020 01:32:18 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> Do you mean ".html5" would be better to be removed?
>> If so, yes.  I just left it because the message would be friendly if it still say "attribute not supported in HTML5".
>
> Sorry, the comment is incorrectly focussed (and annoyingly cryptic: my apologies). 
> I think I was referring to `dc.attr.obsolete.use.css`

I got it.  Ok. Will remove it.

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PR: https://git.openjdk.java.net/jdk/pull/893