system_api: remove cmasone from OWNERS files

Later, kids.

BUG=None
TEST=None

Change-Id: I491c63094ab930a471200aae59a546b8699e0403
Reviewed-on: https://chromium-review.googlesource.com/282750
Commit-Queue: Chris Masone <cmasone@chromium.org>
Trybot-Ready: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>