code: func completeRollingBackRotation(clock clockwork.Clock, ca services.CertAuthority) error {
  	rotation := ca.GetRotation()
  
  	// clean up the state
  	rotation.Started = time.Time{}
  	rotation.State = services.RotationStateStandby
  	rotation.Phase = services.RotationPhaseStandby
  	rotation.Mode = ""
  	rotation.Schedule = services.RotationSchedule{}
  
  	keyPairs := ca.GetTLSKeyPairs()
  	// only keep the original certificate authority as trusted
  	// and remove everything else.
  	keyPairs = []services.TLSKeyPair{keyPairs[0]}
  
  	ca.SetTLSKeyPairs(keyPairs)
  	ca.SetRotation(rotation)
  	return nil
  }
docs: // completeRollingBackRotation completes rollback of the rotation and sets it to the standby state