Replace workaround in doc build that is no longer needed

git-svn-id: https://svn.forgerock.org/opendj/branches/opendj3-server-dev@11082 41b1ffd8-f28e-4786-ab96-9950f0a78031
CR-4738 OPENDJ-1581: Cover disk space thresholds in the Admin Guide

git-svn-id: https://svn.forgerock.org/opendj/branches/opendj3-server-dev@11083 41b1ffd8-f28e-4786-ab96-9950f0a78031