code: void removeBlock(Block block) {
      BlockInfo blockInfo = removeBlockFromMap(block);
      if (blockInfo == null)
        return;
      blockInfo.inode = null;
      for(int idx = blockInfo.numNodes()-1; idx >= 0; idx--) {
        DatanodeDescriptor dn = blockInfo.getDatanode(idx);
        dn.removeBlock(blockInfo); // remove from the list and wipe the location
      }
    }
docs: Remove the block from the block map;
  remove it from all data-node lists it belongs to;
  and remove all data-node locations associated with the block.