Drop slower Node::hasID() / Node::hasClass() methods

Drop slower Node::hasID() / Node::hasClass() methods. Those were here for
convenience but there are very few remaining callers as we use tighter
typing in the code these days. Removing them will encourage future callers
to use tighter typing and call the methods on Element.

This CL updates the 2 remaining call sites to use the methods on Element
instead.

R=abarth@chromium.org, eseidel@chromium.org

Review URL: https://codereview.chromium.org/415243003

git-svn-id: svn://svn.chromium.org/blink/trunk@178885 bbb929c8-8fbe-4397-9dbb-9b2b20218538