Revert of Re-enable fetching component policies for login screen apps (patchset #3 id:40001 of https://codereview.chromium.org/2603463003/ )

Reason for revert:
I'm very sorry I have to revert this since it's breaking device policy updates.

https://bugs.chromium.org/p/chromium/issues/detail?id=679956#c7

Original issue's description:
> Re-enable fetching component policies for login screen apps
>
> This CL relands enabling fetching of policies for Chrome OS login screen
> apps.
>
> The originally landed code was temporarily disabled due to DMServer
> responding with errors when an unknown policy type was requested. Now
> this can be enabled back, after the DMServer got fixed to at least
> ignore the new policy type (until it starts to actually provide policies
> with this type).
>
> BUG=644304,666720
> TEST=re-enabled browser tests;
>      manual test: sign into an enrolled device, go to chrome://policy
>      and check that the device policies were fetched successfully
>
> Committed: https://crrev.com/5eb4901df37717dd05fd071a807a0ebaf563f0f3
> Cr-Commit-Position: refs/heads/master@{#441015}

TBR=emaxx@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=644304,666720

Review-Url: https://codereview.chromium.org/2621413007
Cr-Commit-Position: refs/heads/master@{#443328}
4 files changed