Help: Adapt to Qt >= 6.2

Change-Id: I8529b33c597ab3ea795a6ac599f6f52ae36fce50
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>

src/plugins/help/localhelpmanager.cpp

@@ -401,10 +401,7 @@ QHelpEngine &LocalHelpManager::helpEngine()
         QMutexLocker _(&m_guiMutex);
         if (!m_guiEngine) {
             m_guiEngine = new QHelpEngine(QString());
-#if QT_VERSION >= QT_VERSION_CHECK(6, 0, 0)
             m_guiEngine->setReadOnly(false);
-#endif
-
             m_guiEngine->setUsesFilterEngine(true);
         }
     }