src/main/java/com/conveyal/gtfs/loader/JdbcTableWriter.java
private void deleteFromReferencingTables(String namespace, Table table, int id) throws SQLException {
        updateReferencingTables(namespace, table, id, null);
    }
private void deleteFromReferencingTables(String namespace, Table table, int id) throws SQLException {
        updateReferencingTables(namespace, table, id, null);
    }
Delete entities from any referencing tables (if required). This method is defined for convenience and clarity, but
essentially just runs updateReferencingTables with a null value for newKeyValue param.