Simplify app quitting implementation a bit

app/backend/computermanager.h

@@ -14,8 +14,6 @@
 #include <QSettings>
 #include <QRunnable>
 
-class Session;
-
 class MdnsPendingComputer : public QObject
 {
     Q_OBJECT
@@ -74,7 +72,6 @@ public:
     void pairHost(NvComputer* computer, QString pin);
 
     void quitRunningApp(NvComputer* computer);
-    Q_INVOKABLE void quitRunningApp(Session* session);
 
     QVector<NvComputer*> getComputers();