MXS-1775 MariaDBMonitor::main() removed

Now uses MonitorInstance::main() as all other monitors.

server/modules/monitor/mariadbmon/mariadbmon.hh

@@ -101,7 +101,6 @@ public:
 protected:
     void update_server_status(MXS_MONITORED_SERVER* pMonitored_server);
     void pre_loop();
-    void main();
     void tick();
     void process_state_changes();