Remove old devicekit udisks backend

src/device/deviceinfo.h

@@ -78,7 +78,7 @@ class DeviceInfo : public SimpleTreeItem<DeviceInfo> {
         transcode_format_(Song::FileType_Unknown),
         task_percentage_(-1) {}
 
-  // A device can be discovered in different ways (devicekit, gio, etc.)
+  // A device can be discovered in different ways (udisks2, gio, etc.)
   // Sometimes the same device is discovered more than once.  In this case the device will have multiple "backends".
   struct Backend {
     Backend(DeviceLister *lister = nullptr, const QString &id = QString())