This reverts commit 06e1aa07.

Reason for revert: blocking Skia roll, at least.

Original change's description:
> Generalize git index refresh to bot_update.
> 
> Bug: 746763
> Change-Id: Id0cc8fd672421fe4049334077c6d1e63800524ee
> Reviewed-on: https://chromium-review.googlesource.com/580327
> Commit-Queue: John Budorick <jbudorick@chromium.org>
> Reviewed-by: Robbie Iannucci <iannucci@chromium.org>

TBR=iannucci@chromium.org,dpranke@chromium.org,jbudorick@chromium.org

Change-Id: I834e2acd17417c95d42e18fa26bba822c6f67007
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 746763
Reviewed-on: https://chromium-review.googlesource.com/580767Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>