code: func (whisper *Whisper) DeleteSymKey(id string) bool {
  	whisper.keyMu.Lock()
  	defer whisper.keyMu.Unlock()
  	if whisper.symKeys[id] != nil {
  		delete(whisper.symKeys, id)
  		return true
  	}
  	return false
  }
docs: // DeleteSymKey deletes the key associated with the name string if it exists.