Remove unused SVG functions

This patch removes a smorgasbord of unused SVG functions. Many of these
are fallout of the SVGTearOff rewrite.

BUG=

Review URL: https://codereview.chromium.org/258903003

git-svn-id: svn://svn.chromium.org/blink/trunk@172794 bbb929c8-8fbe-4397-9dbb-9b2b20218538