Fix warning in delegate

The model has no role isDefault. I assume it's a copy and paste from
another model.

src/applet/package/contents/ui/DeviceItem.qml

@@ -29,7 +29,6 @@ PlasmaExtras.ExpandableListItem {
     title: model.DeviceFullName
     subtitle: infoText()
     isBusy: connecting
-    isDefault: model && model.isDefault
     defaultActionButtonAction: Action {
         icon.name: model.Connected ? "network-disconnect" : "network-connect"
         text: model.Connected ? i18n("Disconnect") : i18n("Connect")