ProjectExplorer: De-slot internal class

Missed in 0bf78934.

Change-Id: I91aeb31178bb329266f2c2c79a5e4c54e34d6473
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/projectexplorer/appoutputpane.h

@@ -93,7 +93,7 @@ signals:
      void runControlStarted(ProjectExplorer::RunControl *rc);
      void runControlFinished(ProjectExplorer::RunControl *rc);
 
-public slots:
+public:
     // ApplicationOutput specifics
     void projectRemoved();