CA-111816: Remove duplicate diskdatatest-folder from the sm repository

The sm-repository currently contains the folder diskdatatest although the same
folder is as well contained in the xencert-repository.

As XenCert is the only component that uses diskdatatest, it seems the better
place to maintain it. This commit removes the duplicate copy from SM.

Signed-off-by: Robert Breker <robert.breker@citrix.com>