Revert "USE local lock for buildbot_test_toolchain."

This reverts commit 4260aae2.

Reason for revert: afe_lock_machine is fixed.

Original change's description:
> USE local lock for buildbot_test_toolchain.
> 
> Currently the AFE lock machanism for our nightly test is broken,
> we use local lock as a workaround for now.
> 
> BUG=chromium:762589
> TEST=Generate the crosperf command in another simple python file
>      with the same code. Run the generated command line on
>      crotomation2 and it goes though the locking machine stage.
> 
> Change-Id: Icd3132bc383b63aab6d6f5237a04348f11d8726d
> Reviewed-on: https://chromium-review.googlesource.com/653213


> Commit-Ready: Yunlian Jiang <yunlian@chromium.org>
> Tested-by: Yunlian Jiang <yunlian@chromium.org>
> Reviewed-by: Caroline Tice <cmtice@chromium.org>

Bug: chromium:762589
Change-Id: Ib9f787ff48953d384dd36c72811ebd0f20dd25db
Reviewed-on: https://chromium-review.googlesource.com/1178897


Tested-by: Ting-Yuan Huang <laszio@chromium.org>
Reviewed-by: Luis Lozano <llozano@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>
Commit-Queue: Ting-Yuan Huang <laszio@chromium.org>