Remove outdated code

Change-Id: I65e0ed79dabd987bc67d4082969835d52dd7cb8b
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/utils/launchersocket.cpp

@@ -817,11 +817,7 @@ void LauncherSocket::setSocket(QLocalSocket *socket)
     m_socket.store(socket);
     m_packetParser.setDevice(m_socket);
     connect(m_socket,
-#if (QT_VERSION < QT_VERSION_CHECK(5, 15, 0))
-            static_cast<void(QLocalSocket::*)(QLocalSocket::LocalSocketError)>(&QLocalSocket::error),
-#else
             &QLocalSocket::errorOccurred,
-#endif
             this, &LauncherSocket::handleSocketError);
     connect(m_socket, &QLocalSocket::readyRead,
             this, &LauncherSocket::handleSocketDataAvailable);