Revert "Web Animations: Add CSSAnimatableValueFactory API (partial implementation)"

This reverts commit 3acc2f1dafdacaac2fa76fccf481d3365298b537.
It causes compilation errors.

BUG=
TBR=alancutter

Review URL: https://codereview.chromium.org/21737002

git-svn-id: svn://svn.chromium.org/blink/trunk@155410 bbb929c8-8fbe-4397-9dbb-9b2b20218538