ceph: nuke startsync op

startsync is a no-op, has been for years.  Remove it.

Link: http://tracker.ceph.com/issues/20604


Signed-off-by: Yanhu Cao <gmayyyha@gmail.com>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>