code: boolean removeFromCorruptReplicasMap(Block blk, DatanodeDescriptor datanode) {
      Collection<DatanodeDescriptor> datanodes = corruptReplicasMap.get(blk);
      if (datanodes==null)
        return false;
      if (datanodes.remove(datanode)) { // remove the replicas
        if (datanodes.isEmpty()) {
          // remove the block if there is no more corrupted replicas
          corruptReplicasMap.remove(blk);
        }
        return true;
      }
      return false;
    }
docs: Remove the block at the given datanode from CorruptBlockMap
  @param blk block to be removed
  @param datanode datanode where the block is located
  @return true if the removal is successful;
  false if the replica is not in the map