Revert of If the destination directory doesn't contain the desired repo, delete it

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

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=245530

[Nico, 2014-01-17 16:55:12]

Created Revert of If the destination directory doesn't contain the desired repo,
delete it

[commit-bot: I haz the power, 2014-01-17 16:55:18]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/thakis@chromium.org/141633005/1

[commit-bot: I haz the power, 2014-01-17 16:57:11]

Change committed as 245530