delete kv pair from ns_config_ets_dup if the value is updated with

... delete marker

Change-Id: Ie1622bd236ad57d94080560c403145de69b6ed72
Reviewed-on: http://review.couchbase.org/37010
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>