minor: mark classed that don't allow inheritance as final

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1443389 13f79535-47bb-0310-9956-ffa450edef68
minor: remove unused logger instance

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1443390 13f79535-47bb-0310-9956-ffa450edef68