Revert of Toggle DocumentsUI on/off using ChromeOS flag.

Revert of Toggle DocumentsUI on/off using ChromeOS flag. (patchset #1 id:1 of https://codereview.chromium.org/2804703003/ )

Reason for revert:
Prebundled DocumentsUI no longer being include.

Original issue's description:
> Toggle DocumentsUI on/off using ChromeOS flag.
> 
> Test=manual
> BUG=34847872
> 
> Review-Url: https://codereview.chromium.org/2804703003
> Cr-Commit-Position: refs/heads/master@{#463425}
> Committed: https://chromium.googlesource.com/chromium/src/+/eb85d566226621ba40a61a3e10fa7d6aeae091ad

TBR=hirono@chromium.org,xutan@chromium.org,smckay@chromium.org,stevenjb@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=34847872

[Ben Lin, 2017-05-31 18:35:03]

The CQ bit was checked by linben@chromium.org

[Ben Lin, 2017-05-31 18:35:03]

Created Revert of Toggle DocumentsUI on/off using ChromeOS flag.

[commit-bot: I haz the power, 2017-05-31 18:36:19]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-31 18:36:21]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-31 18:36:22]

No L-G-T-M from a valid reviewer yet.
CQ run can only be started once the patch has received an L-G-T-M from a full
committer.
Even if an L-G-T-M may have been provided, it was from a non-committer,_not_ a
full super star committer.
Committers are members of the group "project-chromium-committers".
Note that this has nothing to do with OWNERS files.

[xutan, 2017-05-31 22:06:36]

Actually https://codereview.chromium.org/2917773002/ already contains this so
there is probably no need for this. That won't compile without this change.