Cleanup .gclient.bot_entries to avoid sync problems on bots.

In https://webrtc-codereview.appspot.com/28509004 the buildbot
case was missed since they get a gclient entries file named
.gclient.bot_entries instead of the regular .gclient_entries
file due to the way the sync was implemented for buildbots.

This change makes the right file get wiped in the two cases.

BUG=
TBR=agable@chromium.org

Review URL: https://webrtc-codereview.appspot.com/28599004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7314 4adac7df-926f-26a2-2b94-8c16560cd09d