Revert of Roll isolate go to binaries as generated by infra @ 6f3db5a82956.

Revert of Roll isolate go to binaries as generated by infra @ 6f3db5a82956. (patchset #1 id:1 of https://codereview.chromium.org/2256093002/ )

Reason for revert:
This is causing isolate step to be much slower per https://bugs.chromium.org/p/chromium/issues/detail?id=644410

Original issue's description:
> Roll isolate go to binaries as generated by infra @ 6f3db5a82956.
> 
> Which is luci-go @ e438e8c3b563e48aaccca7bd0f4997ef29174e3d
> 
> TBR=tansell@chromium.org
> BUG=598990
> 
> Committed: https://crrev.com/a7ce77dda519428ce58039382485c7cd0cc05ab7
> Cr-Commit-Position: refs/heads/master@{#412819}

TBR=tansell@chromium.org,tandrii@chromium.org,maruel@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=598990

[jam, 2016-09-14 19:17:45]

The CQ bit was checked by jam@chromium.org

[jam, 2016-09-14 19:17:45]

Created Revert of Roll isolate go to binaries as generated by infra @
6f3db5a82956.

[commit-bot: I haz the power, 2016-09-14 19:18:36]

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

[jam, 2016-09-14 19:36:44]

ah this was already reverted in https://codereview.chromium.org/2344563003/

[jam, 2016-09-14 19:36:46]

The CQ bit was unchecked by jam@chromium.org