Revert r27579005 "Web Animations CSS: Hook up CSS animation play state"

Breaks Blink waterfall: http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20%28dbg%29/builds/14096

TBR=steveblock
BUG=

Review URL: https://codereview.chromium.org/36883004

git-svn-id: svn://svn.chromium.org/blink/trunk@160341 bbb929c8-8fbe-4397-9dbb-9b2b20218538