Remove Mac cursor images that have moved to Chromium

These resources were migrated to the Chromium repo in
https://src.chromium.org/viewvc/chrome?view=rev&revision=228047

R=abarth@chromium.org
BUG=303964

Review URL: https://codereview.chromium.org/27767002

git-svn-id: svn://svn.chromium.org/blink/trunk@159906 bbb929c8-8fbe-4397-9dbb-9b2b20218538