remove unused ns_config:replace function

Change-Id: Ie3d5e2110e95d988c487916b238629e74e6c3a54
Reviewed-on: http://review.couchbase.org/37005
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>