Revert of Use gclient's git_cache setting in bot_update/api.py (patchset #6 id:100001 of https://codereview.chromium.org/1762513002/ )

Reason for revert:
Roll into build breaks infra crons.

Original issue's description:
> Use gclient's git_cache setting in bot_update/api.py
>
> BUG=589140
> R=agable@chromium.org
>
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=299120

TBR=agable@chromium.org,hinoka@chromium.org,hinoka@google.com,iannucci@chromium.org,wkorman@chromium.org,szager@chromium.org
BUG=589140

Review URL: https://codereview.chromium.org/1776193002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299160 0039d316-1c4b-4281-b951-d872f2087c98