Remove SVGElement::rendererIsNeeded

Remove SVGElement::rendererIsNeeded, the same check is done in RenderTreeBuilder::shouldCreateRenderer.

Review URL: https://codereview.chromium.org/343443003

git-svn-id: svn://svn.chromium.org/blink/trunk@176887 bbb929c8-8fbe-4397-9dbb-9b2b20218538