Remove much of the deadcode in SVG

This patch removes much of the deadcode from core/svg and rendering/svg.
A separate patch will handle the 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/115733002

git-svn-id: svn://svn.chromium.org/blink/trunk@163910 bbb929c8-8fbe-4397-9dbb-9b2b20218538