mbm: remove dead code

plugins/mm-modem-mbm.c

@@ -147,11 +147,8 @@ do_register (MMModemGsmNetwork *modem,
 {
     MMModemMbm *self = MM_MODEM_MBM (modem);
     MMModemMbmPrivate *priv = MM_MODEM_MBM_GET_PRIVATE (self);
-    MMCallbackInfo *info;
     RegisterData *reg_data;
 
-    info = mm_callback_info_new (MM_MODEM (modem), callback, user_data);
-
     reg_data = g_malloc0 (sizeof(RegisterData));
     reg_data->modem = modem;
     reg_data->network_id = network_id;