MB-100: Rest api to delete existing replications

- Earlier api used to cancel older XDCR
replications doesn't exist anymore

Change-Id: Ie60869a52e5d4693d7707e45992ab8815974072a
Reviewed-on: http://review.couchbase.org/26085
Reviewed-by: Tommie McAfee <tommie@couchbase.com>
Tested-by: abhinav dangeti <abhinav.dangeti@gmail.com>