Remove deadcode in the SVG animation system

This patch removes deadcode that's rotting in SVG's animation subsystem.

The list of deadcode was generated using a tool and this patch was
put together manually.

BUG=328627

Review URL: https://codereview.chromium.org/104833008

git-svn-id: svn://svn.chromium.org/blink/trunk@163974 bbb929c8-8fbe-4397-9dbb-9b2b20218538