Ssync_sender bug with creating a delete request

The timestamp that is passed into the send_delete method is a
common.utils.Timestamp. This will cause the headers for the
delete request to not be concatinated. Using the normal property
of the passed timestamp in order to join the headers for the
delete request.

Change-Id: Ib3a1d2ecb5b673fc80ba1f923c2a0c6b0e5b056a