MB-9096: nuked 1.8 replication remains in failover_safeness_level

Change-Id: If64e111c6807859bc56752a3b11a7c1b82b87b95
Reviewed-on: http://review.couchbase.org/29316
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>