Revert "Web Animations: Introduce String based KeyframeEffectModel"

This reverts r170690. Typo in filename breaks the build

TBR=shans
BUG=

Review URL: https://codereview.chromium.org/216603008

git-svn-id: svn://svn.chromium.org/blink/trunk@170697 bbb929c8-8fbe-4397-9dbb-9b2b20218538