code: func dbRemoveTxIndexEntry(dbTx database.Tx, txHash *chainhash.Hash) error {
  	txIndex := dbTx.Metadata().Bucket(txIndexKey)
  	serializedData := txIndex.Get(txHash[:])
  	if len(serializedData) == 0 {
  		return fmt.Errorf("can't remove non-existent transaction %s "+
  			"from the transaction index", txHash)
  	}
  
  	return txIndex.Delete(txHash[:])
  }
docs: // dbRemoveTxIndexEntry uses an existing database transaction to remove the most
  // recent transaction index entry for the given hash.