Removing all dependencies to QtXmlPatterns for compatibility with Qt6

This is issue 887 and is unfortunately required in order to compile on Apple Arm
silicon...

src/main/XMLReader.cc

@@ -23,8 +23,6 @@
 #include <src/main/inishell.h>
 
 #include <QCoreApplication> //for translations
-#include <QtXmlPatterns/QXmlSchema>
-#include <QtXmlPatterns/QXmlSchemaValidator>
 
 /**
  * @class XMLReader
@@ -87,7 +85,6 @@ QString XMLReader::read(QFile &file, QString &xml_error, const bool &no_referenc
 		return QString();
 
 	parseIncludes(xml_, master_xml_file_, xml_error); //"<include file='...'/>" tags
-	validateSchema(xml_error);
 	parseReferences(); //"<reference name='...'/>" tags
 	return parseAutoloadIni();
 }
@@ -259,31 +256,3 @@ QDomDocument XMLReader::getXml() const
 	return xml_;
 }
 
-/**
- * @brief Perform schema validation on an XML file.
- * @param[out] xml_error XML operations error string to add to.
- */
-void XMLReader::validateSchema(QString &xml_error) const
-{
-	/*
-	 * The logger already displays a lot of info and the XML parser itself also logs errors,
-	 * but what it doesn't do is check for outdated parameter names, unknown attributes, etc.,
-	 * so the schema validation is still useful.
-	 */
-	MessageHandler msgHandler;
-	QXmlSchema schema;
-	schema.setMessageHandler(&msgHandler);
-	schema.load( QUrl("qrc:config_schema.xsd") );
-	if (!schema.isValid()) {
-		xml_error += QCoreApplication::tr("XML error: there is an error in the internal xsd file. Skipping schema validation.") + "\n";
-	} else {
-		const QXmlSchemaValidator validator(schema);
-		const bool validation_success = validator.validate(xml_.toString().toUtf8());
-		if (!validation_success) {
-			QTextDocument error_msg;
-			error_msg.setHtml(msgHandler.status()); //strip HTML
-			xml_error += "[XML error: schema validation failed] " + error_msg.toPlainText() +
-			    QString(" (line %1, column %2)").arg(msgHandler.line(), msgHandler.column()) + "\n";
-		}
-	}
-}

src/main/XMLReader.h

@@ -62,8 +62,6 @@ class XMLReader {
 #endif //def DEBUG
 
 	private:
-		void validateSchema(QString &xml_error) const;
-
 		QString master_xml_file_;
 		QDomDocument xml_;
 };