remove dead cleanup code.

remove dead cleanup code.

13836        if (zone != NULL)
13837                dns_zone_detach(&zone);

     	null: At condition dz != NULL, the value of dz must be NULL.
     	dead_error_condition: The condition dz != NULL cannot be true.

13838        if (dz != NULL) {

	CID 1453456 (#1 of 1): Logically dead code (DEADCODE)
	dead_error_begin: Execution cannot reach this statement:
	dns_zone_detach(&dz->zone);.

13839                dns_zone_detach(&dz->zone);
13840                isc_mem_put(named_g_mctx, dz, sizeof(*dz));
13841        }