Revert r1433756: HDFS-4288. NN accepts incremental BR as IBR in safemode. Contributed by Daryn Sharp.

This commit caused TestBlockManager to fail.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1433821 13f79535-47bb-0310-9956-ffa450edef68