The package hibernate-envers.jar used to have this class. Now it doesn't anymore

Neither does hibernate-tools.jar

However documentation still seems to refer to it.

http://docs.jboss.org/hibernate/orm/4.3/javadocs/org/hibernate/tool/ant/EnversHibernateToolTask.html

Chapter 15.10:
http://docs.jboss.org/hibernate/orm/4.3/devguide/en-US/html/ch15.html

If you'd like to generate the database schema file with the Hibernate Tools Ant task, you'll probably notice that the generated file doesn't contain definitions of audit tables. To generate also the audit tables, you simply need to use org.hibernate.tool.ant.EnversHibernateToolTask instead of the usual org.hibernate.tool.ant.HibernateToolTask. The former class extends the latter, and only adds generation of the version entities. So you can use the task just as you used to.