Remove unnecessary workaround in universal-accelerated-overflow-scrolling.html.

The issue that required this workaround was fixed in
https://codereview.chromium.org/204983002/.

BUG=328156

Review URL: https://codereview.chromium.org/209963003

git-svn-id: svn://svn.chromium.org/blink/trunk@169853 bbb929c8-8fbe-4397-9dbb-9b2b20218538