ignore only linkage, not system

jastadd-mquat-eris/src/main/java/de/tudresden/inf/st/mquat/eris/ErisMQuATBuilder.java

@@ -236,8 +236,8 @@ public class ErisMQuATBuilder {
       for (ERISContainer erisContainer : erisModel.getErisContainers()) {
         for (ERISAttribute attribute : erisContainer.getAttributeList()) {
 
-          // TODO check if system attributes really can be ignored
-          if (attribute.isSystem()) continue;
+          // ignore linkage attributes
+          if (attribute.isLinkage()) continue;
 
           // ignore attribute if all stats are zero
           ERISAttributeStatistics stats = attribute.getStatistics();