Delete the QNetworkAccessManager when we're done with it

Apparently having this object around can lead to background
network scans happening that cause WiFi perf degradation.

app/backend/autoupdatechecker.h

@@ -25,5 +25,5 @@ private:
     QString getPlatform();
 
     QVector<int> m_CurrentVersionQuad;
-    QNetworkAccessManager m_Nam;
+    QNetworkAccessManager* m_Nam;
 };