code: func (bk *Backend) DeleteKey(bucket []string, key string) error {
  	// Open the bucket to work on the items.
  	b, err := bk.openBucket(bk.flatten(bucket), os.O_RDWR)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	defer b.Close()
  
  	// If the key doesn't exist, return trace.NotFound.
  	_, ok := b.getItem(key)
  	if !ok {
  		return trace.NotFound("key %v not found", key)
  	}
  
  	// Otherwise, delete key.
  	b.deleteItem(key)
  
  	return nil
  }
docs: // DeleteKey deletes a key in a bucket.