Remove --enable-accelerated-filters flag, Blink-side.

This removes all the support code, and the legacy Blink-side accelerated
filter rendering.

Acceleration of SVG-on-SVG filters will be achieved instead with
deferred filters, impl-side painting and Ganesh rasterization.
(CSS filters have their own layer-based accelerated rendering
path, implemented in the compositor, which is already shipping.)

NOTE: this change depends on the Chrome-side change
https://codereview.chromium.org/205923005/, which must land first.

BUG=196562
R=junov@chromium.org

Review URL: https://codereview.chromium.org/205033010

git-svn-id: svn://svn.chromium.org/blink/trunk@169707 bbb929c8-8fbe-4397-9dbb-9b2b20218538