Remove obsolete documentation from realm package javadoc.
The text is something very old that talks about "debug" attribute and that there are two standard realms, JDBCRealm and MemoryRealm.
The up-to-date documentation is maintained in docs/config/realm.html

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1601855 13f79535-47bb-0310-9956-ffa450edef68