Fix example to use item returned by PlotWidget.add*

Author: t20100

examples/plotWidget.py

@@ -160,8 +160,7 @@ def showDelaunay(self):
         x = numpy.random.rand(nbPoints)
         y = numpy.random.rand(nbPoints)
         value = numpy.random.rand(nbPoints)
-        legend = plot.addScatter(x=x, y=y, value=value)
-        scatter = plot.getScatter(legend)
+        scatter = plot.addScatter(x=x, y=y, value=value)
         scatter.setVisualization("solid")
         plot.resetZoom()