code: func (b *EtcdBackend) Delete(ctx context.Context, key []byte) error {
  	start := b.clock.Now()
  	re, err := b.client.Delete(ctx, prependPrefix(key))
  	writeLatencies.Observe(time.Since(start).Seconds())
  	writeRequests.Inc()
  	if err != nil {
  		return trace.Wrap(convertErr(err))
  	}
  	if re.Deleted == 0 {
  		return trace.NotFound("%q is not found", key)
  	}
  	return nil
  }
docs: // Delete deletes item by key