[Mac] Remove NSScreen renderer sandbox warmup.

This should no longer be necessary now that the scrollbar animations are
no longer driven by NSAnimation (https://codereview.chromium.org/529103002/).

BUG=306348,533537
R=avi@chromium.org

Review-Url: https://codereview.chromium.org/2509273005
Cr-Commit-Position: refs/heads/master@{#434775}
37 files changed