fix the QML demo

Zhao Yuhang

2025-02-09 f1d4f07dcb8bd93578abb2fc1e289050d7e1c3ee

 examples/mainwindow/mainwindow.h

@@ -30,8 +30,6 @@
protected:
    bool event(QEvent *event) override;

    void closeEvent(QCloseEvent *event) override;

private:
    void installWindowAgent();
    void loadStyleSheet(Theme theme);