LUCENE-5858: clear bogus code/comment up

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5858@1621790 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5858: remove impersonation

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5858@1621805 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5858: don't even register RW test codecs, impersonation is removed

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene5858@1621807 13f79535-47bb-0310-9956-ffa450edef68