LUCENE-5953: Remove obsolete locking


git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1637688 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5953: Fix null lock factory

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1637701 13f79535-47bb-0310-9956-ffa450edef68