Revert "Wizards: Accept asynchronous root components for qqapplication"

This reverts commit dcb8681cb7.

The effort to handle asynchronous loading is not required for the
qmllivepreview (for which it had been introduced).

Task-number: QTCREATORBUG-19648
Change-Id: I20cbd318dedb3da43d4993c0c0a1910ffe6d5761
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

share/qtcreator/templates/wizards/projects/qtquickapplication/main.cpp

@@ -20,25 +20,9 @@ int main(int argc, char *argv[])
     QGuiApplication app(argc, argv);
 
     QQmlApplicationEngine engine;
-
-    const QUrl mainQml(QStringLiteral("qrc:/main.qml"));
-
-    // Catch the objectCreated signal, so that we can determine if the root component was loaded
-    // successfully. If not, then the object created from it will be null. The root component may
-    // get loaded asynchronously.
-    const QMetaObject::Connection connection = QObject::connect(
-                &engine, &QQmlApplicationEngine::objectCreated,
-                &app, [&](QObject *object, const QUrl &url) {
-        if (url != mainQml)
-            return;
-
-        if (!object)
-            app.exit(-1);
-        else
-            QObject::disconnect(connection);
-    }, Qt::QueuedConnection);
-
-    engine.load(mainQml);
+    engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
+    if (engine.rootObjects().isEmpty())
+        return -1;
 
     return app.exec();
 }