Remove blink::isWindowsVistaOrGreater.

Chromium no longer supports Windows XP; see:
  https://code.google.com/p/chromium/issues/detail?id=579196

BUG=579265

Review URL: https://codereview.chromium.org/1609083002

Cr-Commit-Position: refs/heads/master@{#372373}
4 files changed