Remove the SVGColor and SVGPaint DOM interfaces (were deprecated).
Spec: http://www.w3.org/TR/SVG11/svgdom.html#ExtendedInterfaces
SVG2 spec removal: https://svgwg.org/svg2-draft/changes.html#svgdom

Change test expectations, serialize colors as CSS component values, aka
the same way as the 'color' property. Opera (Presto) and Firefox already
use that way of serializing SVGColor/SVGPaint values.
CSSOM WD spec for serializing <color> values:
http://dev.w3.org/csswg/cssom/#serialize-a-css-component-value

This is to prepare for rewriting the SVG side, removing the respective
classes there too.

BUG=329518
R=pdr, krit, schenney

Review URL: https://codereview.chromium.org/114373004

git-svn-id: svn://svn.chromium.org/blink/trunk@164179 bbb929c8-8fbe-4397-9dbb-9b2b20218538