Revert "Generalize git index refresh to bot_update."

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>

recipes/recipe_modules/bot_update/resources/bot_update.py

@@ -1139,17 +1139,6 @@ def main():
 
   solutions_printer(git_slns)
 
-  # Creating hardlinks during a build can interact with git reset in
-  # unfortunate ways if git's index isn't refreshed beforehand. (See
-  # crbug.com/330461#c13 for an explanation.)
-  try:
-    call_gclient(['recurse', '-v', 'git', 'update-index', '--refresh'])
-  except SubprocessFailed:
-    # Failure here (and nowhere else) may have adverse effects on the
-    # compile time of the build but shouldn't affect its ability to
-    # successfully complete.
-    print 'WARNING: Failed to update git indices.'
-
   try:
     # Dun dun dun, the main part of bot_update.
     revisions, step_text, shallow = prepare(options, git_slns, active)