SampleValidator::validateInterferences: remove the Windows-specific error for Xi integration

With GSL v2.7.1 the Xi integration can be performed under Windows.

Resolves issue #160

GUI/Model/Sample/SampleValidator.cpp

@@ -36,24 +36,6 @@ void SampleValidator::validateItem(const ItemWithParticles* item)
 void SampleValidator::validateInterferences(const LayerItem* layer)
 {
     ASSERT(layer);
-#ifdef WIN32
-
-    int iLayout = 0;
-    for (const auto* layout : layer->layoutItems()) {
-        iLayout++;
-        if (const auto* c = dynamic_cast<const Interference2DAbstractLatticeItem*>(
-                layout->interferenceSelection().currentItem()))
-            if (c->xiIntegration()) {
-                const QString message =
-                    QString("Interference function of layer '%1', Particle layout %2: "
-                            "Integration over Xi is currently not supported "
-                            "under Windows")
-                        .arg(layer->layerName())
-                        .arg(iLayout);
-                addMessage(message);
-            }
-    }
-#endif
 }
 
 void SampleValidator::addMessage(const QString& m)