adjust to Qt 5.14.x; remove compiler warnings.

src/musredit_qt5/musredit/PMusrEditAbout.cpp

@@ -34,7 +34,7 @@
 /**
  * <p>Handles the musredit about popup.
  */
-PMusrEditAbout::PMusrEditAbout(QWidget *parent, Qt::WindowFlags f) : QDialog(parent, f)
+PMusrEditAbout::PMusrEditAbout(QWidget *parent) : QDialog(parent)
 {
   setupUi(this);