ModeManager: Remove old API that was used by old progress manager

Change-Id: Ia4083beb0b4a3eddc906af1b79e8bd5e6a36e47b
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

src/plugins/coreplugin/modemanager.h

@@ -60,7 +60,6 @@ public:
 
     static void addAction(QAction *action, int priority);
     static void addProjectSelector(QAction *action);
-    static void addWidget(QWidget *widget);
 
     static void activateMode(Id id);
     static void setFocusToCurrentMode();