Update the column names (github#1022)

* updated the column names

* reverted add_dimension change

Co-authored-by: Lana Brindley <github@lanabrindley.com>

timescaledb/how-to-guides/user-defined-actions/example-generic-retention.md

@@ -18,7 +18,7 @@ BEGIN
     RAISE EXCEPTION 'Config must have drop_after';
   END IF;
 
-  PERFORM drop_chunks(format('%I.%I', table_schema, table_name), older_than => drop_after)
+  PERFORM drop_chunks(format('%I.%I', hypertable_schema, hypertable_name), older_than => drop_after)
     FROM timescaledb_information.hypertables;
 END
 $$;