Revert "Implement enableFastMobileScrolling web api."

Breaks incremental builds.

BUG=381391
TBR=peter@chromium.org

Review URL: https://codereview.chromium.org/312423006

git-svn-id: svn://svn.chromium.org/blink/trunk@175684 bbb929c8-8fbe-4397-9dbb-9b2b20218538