This reverts commit 58ff145e.

Reason for revert: the bug in git-numberer has been fixed and deployed.

Original change's description:
> [release] Temporarily disable gerrit for merge tools.
> 
> BUG=chromium:698845
> NOTRY=true
> TBR=hablich@chromium.org,tandrii@chromium.org
> 
> Change-Id: I970c984c5e9bd23ca3d951d13243d107fc2a2e3f
> Reviewed-on: https://chromium-review.googlesource.com/451280
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Reviewed-by: Michael Hablich <hablich@chromium.org>
> Commit-Queue: Michael Hablich <hablich@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#43646}

R=machenbach@chromium.org,hablich@chromium.org
# Not skipping CQ checks because original CL landed > 1 day ago.
BUG=chromium:698845

Change-Id: I34b12a36c21a2d7a46eb67bce0536298a0582dd5
Reviewed-on: https://chromium-review.googlesource.com/455799Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43840}