SVGStyledElement::getPresentationAttribute() does not need to be virtual.

From Blink r149888 by <cevans@chromium.org>
<http://src.chromium.org/viewvc/blink?view=revision&revision=149888>

* svg/SVGStyledElement.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@149734 268f45cc-cd09-0410-ab3c-d52691b4dbfc