Remove MGS policy overrides when they have cloud values

Bug: b:186736957
Change-Id: I9f0cbfdbcfa4d7713d55446f17058a35f9ad94c2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2983202


Commit-Queue: Maria Petrisor <mpetrisor@chromium.org>
Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#899021}