code: func (s *sentFolderDownloadState) destroy() []protocol.FileDownloadProgressUpdate {
  	updates := make([]protocol.FileDownloadProgressUpdate, 0, len(s.files))
  	for name, info := range s.files {
  		updates = append(updates, protocol.FileDownloadProgressUpdate{
  			Name:       name,
  			Version:    info.version,
  			UpdateType: protocol.UpdateTypeForget,
  		})
  		delete(s.files, name)
  	}
  	return updates
  }
docs: // destroy removes all stored state, and returns a set of updates we need to
  // dispatch to clean up the state on the remote end.