Remove unused method and de-virtualize others in Element.h

Remove unused method and de-virtualize others in Element.h
https://bugs.webkit.org/show_bug.cgi?id=115770

Reviewed by Andreas Kling.

Merge https://chromium.googlesource.com/chromium/blink/+/c2c2ff9cb69f46f5cc9d289b2bfbdb8ab5bd3e49

The de-virtualization possibilities were noted whilst "FINALizing" the Node
hierarchy. If a method is successfully marked FINAL but then fails when marked
OVERRIDE as well, the method by definition does not need to be virtual.

* WebCore.exp.in:
* dom/Element.h:
(WebCore::Element::hasAuthorShadowRoot):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@149718 268f45cc-cd09-0410-ab3c-d52691b4dbfc