Remove [LegacyTreatAsPartialInterface] from SVGTests

Also:
* Remove SVG 1.1 cruft:
SVGUseElement implements SVGTests;

...since implemented by parent:
interface SVGUseElement : SVGGraphicsElement { ... };
SVGGraphicsElement implements SVGTests;

R=haraken
BUG=360435

Review URL: https://codereview.chromium.org/226623010

git-svn-id: svn://svn.chromium.org/blink/trunk@171023 bbb929c8-8fbe-4397-9dbb-9b2b20218538