Reland "Remove MGS policy overrides when they have cloud values"

This is a reland of 6a139b5b

Original change's description:
> 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}

Bug: b:186736957
Change-Id: Ie37b39bf7578c42cba86919509128d26ef840195
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3014036


Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Reviewed-by: Dominique Fauteux-Chapleau <domfc@chromium.org>
Commit-Queue: Maria Petrisor <mpetrisor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#899565}