Merge pull request #214 from keijiro/fix-delete-node

Clear node selection when deleting nodes.

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Drawing/Views/MaterialGraphView.cs

                     graph.RemoveShaderProperty(property.guid);
                 }
             }
+            selection.Clear();
         }
 
         public bool CanAcceptDrop(List<ISelectable> selection)