Fixed compilation with older qt versions

plugins/advancedviewplugin/dialogs/bookingdialog.cpp

@@ -6,7 +6,12 @@ BookingDialog::BookingDialog(QWidget *parent) :
     ui(new Ui::BookingDialog)
 {
     ui->setupUi(this);
+
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 9, 0))
     setWindowFlag(Qt::WindowContextHelpButtonHint, false);
+#else
+    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
+#endif
 }
 
 BookingDialog::~BookingDialog()

plugins/advancedviewplugin/dialogs/timeassignmentdialog.cpp

@@ -13,7 +13,12 @@ TimeAssignmentDialog::TimeAssignmentDialog(const QMap<QString, QString> &project
     ui(new Ui::TimeAssignmentDialog)
 {
     ui->setupUi(this);
+
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 9, 0))
     setWindowFlag(Qt::WindowContextHelpButtonHint, false);
+#else
+    setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
+#endif
 
     {
         for(const auto &preferedProject : settings.projects())