Don't use removed QTextStream::setCodec()

QTextStream encodes as UTF-8 by default.

src/app/filelogger.cpp

@@ -126,7 +126,9 @@ void FileLogger::addLogMessage(const Log::Msg &msg)
     if (!m_logFile.isOpen()) return;
 
     QTextStream stream(&m_logFile);
+#if (QT_VERSION < QT_VERSION_CHECK(6, 0, 0))
     stream.setCodec("UTF-8");
+#endif
 
     switch (msg.type)
     {