code: func (fs *FSLocalKeyStore) DeleteKey(host string, username string) error {
  	dirPath, err := fs.dirFor(host, false)
  	if err != nil {
  		return trace.Wrap(err)
  	}
  	files := []string{
  		filepath.Join(dirPath, username+fileExtCert),
  		filepath.Join(dirPath, username+fileExtTLSCert),
  		filepath.Join(dirPath, username+fileExtPub),
  		filepath.Join(dirPath, username),
  	}
  	for _, fn := range files {
  		if err = os.Remove(fn); err != nil {
  			return trace.Wrap(err)
  		}
  	}
  	return nil
  }
docs: // DeleteKey deletes a key from the local store