typo, wording

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1476126 13f79535-47bb-0310-9956-ffa450edef68
OAK-781: Clarify / fix effects of MISSING_NODE as base state of NodeBuilder
remove unused method

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1476127 13f79535-47bb-0310-9956-ffa450edef68