ImageViewer: Use standard plugin setup pattern

Change-Id: Iab9536115b243563bb9a4bfd56b9d211a45f1b0b
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/imageviewer/imageviewerfactory.h

@@ -37,7 +37,7 @@ class ImageViewerFactory : public Core::IEditorFactory
 {
     Q_OBJECT
 public:
-    explicit ImageViewerFactory(QObject *parent = nullptr);
+    ImageViewerFactory();
 
     Core::IEditor *createEditor() override;
 };