Move service user injection into MySQL authenticator

The MySQL authenticator now injects the service user into the list of
allowed users if loading of database users fails. This allows the removal
of common code in the binlogrouter and maxinfo modules.

server/core/service.c

@@ -303,7 +303,6 @@ serviceStartPort(SERVICE *service, SERV_LISTENER *port)
 
     /** Load the authentication users before before starting the listener */
     if (port->listener->authfunc.loadusers &&
-        (service->router->getCapabilities() & RCAP_TYPE_NO_USERS_INIT) == 0 &&
         port->listener->authfunc.loadusers(port) != MXS_AUTH_LOADUSERS_OK)
     {
         MXS_ERROR("[%s] Failed to load users for listener '%s', authentication might not work.",