code: func (vl VersionList) pop(device []byte) (VersionList, FileVersion, int) {
  	removedAt := -1
  	for i, v := range vl.Versions {
  		if bytes.Equal(v.Device, device) {
  			vl.Versions = append(vl.Versions[:i], vl.Versions[i+1:]...)
  			return vl, v, i
  		}
  	}
  	return vl, FileVersion{}, removedAt
  }
docs: // pop returns the VersionList without the entry for the given device, as well
  // as the removed FileVersion and the position, where that FileVersion was.
  // If there is no FileVersion for the given device, the position is -1.