code: INode unprotectedDelete(String src, long modificationTime) {
      return unprotectedDelete(src, this.getExistingPathINodes(src), null,
          BLOCK_DELETION_NO_LIMIT, modificationTime);
    }
docs: Delete a path from the name space
  Update the count at each ancestor directory with quota
  @param src a string representation of a path to an inode
  @param modificationTime the time the inode is removed
  @return the deleted target inode, null if deletion failed