Revert of bot_update: call gclient sync after checking out a gerrit ref (patchset #1 id:1 of https://codereview.chromium.org/1904663002/ )

Reason for revert:
I believe this is mostly likely to have broken Angle, but this is speculative.

http://crbug.com/606150

Original issue's description:
> bot_update: call gclient sync after checking out a gerrit ref
> 
> BUG=chromium:602906
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=300109

TBR=hinoka@chromium.org,yyanagisawa@chromium.org,hinoka@google.com,phajdan.jr@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:602906

Review URL: https://codereview.chromium.org/1918903003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@300159 0039d316-1c4b-4281-b951-d872f2087c98