LibWeb: Make :link selector behave according to spec

It should match any `a` or `area` element that has an `href` attribute,
not any element *inside* an enclosing linked element.

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -244,11 +244,6 @@ void Node::invalidate_style()
     document().schedule_style_update();
 }
 
-bool Node::is_link() const
-{
-    return enclosing_link_element();
-}
-
 String Node::child_text_content() const
 {
     if (!is<ParentNode>(*this))