LUCENE-6025: Give AbstractPagedMutable the accountable interface

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1634588 13f79535-47bb-0310-9956-ffa450edef68
remove redundant/outdated check

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1634589 13f79535-47bb-0310-9956-ffa450edef68