code: func dropBlockIDIndex(db database.DB) error {
  	return db.Update(func(dbTx database.Tx) error {
  		meta := dbTx.Metadata()
  		err := meta.DeleteBucket(idByHashIndexBucketName)
  		if err != nil {
  			return err
  		}
  
  		return meta.DeleteBucket(hashByIDIndexBucketName)
  	})
  }
docs: // dropBlockIDIndex drops the internal block id index.