Web Animations CSS: Remove unused integer clamp routines 

Use the template added in Blink r157590 instead. No behavioral
change. Covered by existing tests.

Review URL: https://chromiumcodereview.appspot.com/23542030

git-svn-id: svn://svn.chromium.org/blink/trunk@157815 bbb929c8-8fbe-4397-9dbb-9b2b20218538