Revert of If the destination directory doesn't contain the desired repo, delete it (https://codereview.chromium.org/61623008/)

Reason for revert:
This breaks `gclient sync` for me. Before this patch:
________ found .git directory; skipping src

After this patch:
Error: 1> Can't update/checkout /Volumes/MacintoshHD2/src/chrome-git/src if an unversioned directory is present. Delete the directory and try again.


Original issue's description:
> If the destination directory doesn't contain the desired repo, delete it
> 
> Basic functionality - this may not be in quite the right place.
> 
> Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=245404

TBR=iannucci@chromium.org,ilevy@chromium.org,cmp@chromium.org,maruel@chromium.org,morrita@chromium.org,borenet@google.com
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/141633005

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@245530 0039d316-1c4b-4281-b951-d872f2087c98