UI: Remove QNetworkReply from window-basic-main.hpp

QNetworkReply was added here in commit
5ba8b09c9c0ee3bd4cca7860e5892ee60d1f6cf6. Qt5Network was replaced in
commits 13bed1a448e3726819778e5759bdf456556b6bf9 and
39d1cda4e9b276f1b0770027e211aec0d9ecb927, but this one line referring to
QNetworkReply remained. Let's finally remove it.

UI/window-basic-main.hpp

@@ -42,7 +42,6 @@
 class QMessageBox;
 class QListWidgetItem;
 class VolControl;
-class QNetworkReply;
 class OBSBasicStats;
 
 #include "ui_OBSBasic.h"