SVGElement::parseAttribute resolves property via property map (Step 2)

This is to replace the existing |SVGElement::parseAttribute| implementation,
but as there are many callers, we would like to proceed this incrementally.
a) Introduce |SVGElement::parseAttributeNew| *LANDED*
b) Convert all overrides |SVGElement::parseAttribute| to
   a |parseAttributeNew| call. <-- This patch
c) Replace existing |parseAttribute| with |parseAttributeNew|, and remove all
   overrides simply calling |parseAttributeNew|

This patch is (b).

Bonus: Remove {parseAttribute,isSupportedAttribute,svgAttributeChanged} on SVGGElement which was a noop.

BUG=397902

Review URL: https://codereview.chromium.org/420193011

git-svn-id: svn://svn.chromium.org/blink/trunk@179105 bbb929c8-8fbe-4397-9dbb-9b2b20218538