UI: Use OBS dock menu instead of Qt dock context menu

UI/window-basic-main.hpp

@@ -834,6 +834,8 @@ private slots:
 	void on_actionVerticalCenter_triggered();
 	void on_actionHorizontalCenter_triggered();
 
+	void on_customContextMenuRequested(const QPoint &pos);
+
 	void on_scenes_currentItemChanged(QListWidgetItem *current,
 					  QListWidgetItem *prev);
 	void on_scenes_customContextMenuRequested(const QPoint &pos);