info-overview: Don't show "Firmware Version" row in virtual machines

This value comes from systemd-hostnamed, which harvests it from
/sys/class/dmi/id/bios_version, which happens to be empty/invalid
in virtual machines (at least KVM powered virtualization).

For this reason, we are better off hiding the "Firmware Version"
row when gnome-control-center is running in a VM.

Fixes #2181

panels/info-overview/cc-info-overview-panel.c

@@ -553,6 +553,8 @@ set_virtualization_label (CcInfoOverviewPanel *self,
   if (virt == NULL || *virt == '\0')
     {
       gtk_widget_hide (GTK_WIDGET (self->virtualization_row));
+      gtk_widget_hide (GTK_WIDGET (self->firmware_version_row));
+
       return;
     }