Disable animated clipping on SVG content

Animated clipping has to be disabled until it is not supported properly.
With removing the clip property from animatedPropertyTypeForCSSAttribute
animted clipping is considered as an unknown animation and won't cause
assertion failure later.

R=kouhei@chromium.org,fs@opera.com
BUG=422955

Review URL: https://codereview.chromium.org/656443002

git-svn-id: svn://svn.chromium.org/blink/trunk@183671 bbb929c8-8fbe-4397-9dbb-9b2b20218538