修复VO字段重复导致LogAspect报错，无法创建章节

mooctest-site-server/src/main/java/cn/iselab/mooctest/site/web/data/EntityVO.java

@@ -15,5 +15,4 @@ public class EntityVO {
     private long entityId;
     private EntityTypeEnum entityType;
     private int sortedId;
-    private boolean previewable;
 }