code: func (p *Plugin) DeleteMemory(in *Msg, k string) {
  	var err error
  	if in.User.ID > 0 {
  		q := `DELETE FROM states
  		      WHERE userid=$1 AND pluginname=$2 AND key=$3`
  		_, err = p.DB.Exec(q, in.User.ID, p.Config.Name, k)
  	} else {
  		q := `DELETE FROM states
  		      WHERE flexid=$1 AND flexidtype=$2 AND pluginname=$3
  		      AND key=$4`
  		_, err = p.DB.Exec(q, in.User.FlexID, in.User.FlexIDType,
  			p.Config.Name, k)
  	}
  	if err != nil {
  		p.Log.Infof("could not delete memory for key %s. %s", k,
  			err.Error())
  	}
  }
docs: // DeleteMemory deletes a memory for a given key. It is not an error to delete
  // a key that does not exist.