code: public void deleteRelationshipIndex(EntityMetadata entityMetadata, GraphDatabaseService graphDb,
              Relationship relationship)
      {
          if (!isRelationshipAutoIndexingEnabled(graphDb) && entityMetadata.isIndexable())
          {
              Index<Relationship> relationshipIndex = graphDb.index().forRelationships(entityMetadata.getIndexName());
              relationshipIndex.remove(relationship);
          }
      }
docs: Deletes a {@link Relationship} from manually created index if
  auto-indexing is disabled
  
  @param entityMetadata
  @param graphDb
  @param relationship