D23901: Remove the HTML/CSS validation plug-in

[Volker Krause]

vkrause added a task: T11543: Port Konqueror away from KHTML.

REPOSITORY
  R226 Konqueror

REVISION DETAIL
  https://phabricator.kde.org/D23901

To: vkrause, dfaure
Cc: kde-doc-english, gennad, fbampaloukas, skadinna