Reduce size of ExportCollection for about 50%

src/AddIns/Misc/Reports/ICSharpCode.Reports.Core/Project/Collections/Collections.cs

@@ -355,15 +355,12 @@ namespace ICSharpCode.Reports.Core{
 	}
 	
 	#region ExporterCollection
+	
 	public class ExporterCollection : Collection<BaseExportColumn>
 	{
 		
 		public void AddRange (IEnumerable <BaseExportColumn> items){
 			foreach (var item in items) {
-				IExportContainer container = item as IExportContainer;
-				if (container != null) {
-					AddRange(container.Items);
-				}
 				this.Add (item);
 			}
 		}