Revert of MD Settings: enable by default in client (patchset #4 id:60001 of https://codereview.chromium.org/2699973002/ )

Reason for revert:
BUG=694081

It broke ChromeOS tests and thus blocked Chrome roll to ChromeOS.
In my personal opinion, what really needs fix are the tests rather than the change,
but the changes to the tests looks far nontrivial.
For now, allow me to revert this change to unblock the divergence between Chrome and ChromeOS ToT...

Original issue's description:
> MD Settings: enable by default in client
>
> R=dpapad@chromium.org
> BUG=478982
>
> Review-Url: https://codereview.chromium.org/2699973002
> Cr-Commit-Position: refs/heads/master@{#451338}
> Committed: https://chromium.googlesource.com/chromium/src/+/a8109d958f144e541a204da6debd820d936d6108

TBR=dpapad@chromium.org,sky@chromium.org,dbeam@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=478982

Review-Url: https://codereview.chromium.org/2703283002
Cr-Commit-Position: refs/heads/master@{#451684}
10 files changed