Remove unused HTMLTextFormControlElement::textRendererAfterUpdateLayout

Nothing uses this method, we should just remove it.

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

Review URL: https://chromiumcodereview.appspot.com/19136002

git-svn-id: svn://svn.chromium.org/blink/trunk@154180 bbb929c8-8fbe-4397-9dbb-9b2b20218538