Tests.QmlDesigner: fix loadEmptyCoreModel()

Attaching more then one rewriter is not a good idea.

Change-Id: I3ec000836dc21029b43003c4636927086f267d10
Reviewed-by: Marco Bubke <marco.bubke@digia.com>

tests/auto/qml/qmldesigner/coretests/tst_testcore.cpp

@@ -203,7 +203,7 @@ void tst_TestCore::loadEmptyCoreModel()
     textEdit1.setPlainText(file.readAll());
     NotIndentingTextEditModifier modifier1(&textEdit1);
 
-    QScopedPointer<Model> model1(createModel("QtQuick.Item"));
+    QScopedPointer<Model> model1(Model::create("QtQuick.Item"));
 
     QScopedPointer<TestRewriterView> testRewriterView1(new TestRewriterView());
     testRewriterView1->setTextModifier(&modifier1);