Update Javadoc, as addValve/removeValve methods belong to Pipeline.

The addValve() method is still here (to be called by digester),
but ContainerBase.removeValve() has been removed in Tomcat 7.

This staleness in Javadoc has been noted on the users mailing list.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1588462 13f79535-47bb-0310-9956-ffa450edef68