Lose method WebRange::textQuads().

It is never called, and dropping it allows us to lose an entire type
from the public interface.

R=jochen@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/430113002

git-svn-id: svn://svn.chromium.org/blink/trunk@179503 bbb929c8-8fbe-4397-9dbb-9b2b20218538