Remove stale comment about TI index (#39470)
The index this comment is talking about was removed in #30762.
diff --git a/airflow/models/taskinstance.py b/airflow/models/taskinstance.py
index 4e095e7..ef2a41a 100644
--- a/airflow/models/taskinstance.py
+++ b/airflow/models/taskinstance.py
@@ -1387,14 +1387,6 @@
Index("ti_dag_run", dag_id, run_id),
Index("ti_state", state),
Index("ti_state_lkp", dag_id, task_id, run_id, state),
- # The below index has been added to improve performance on postgres setups with tens of millions of
- # taskinstance rows. Aim is to improve the below query (it can be used to find the last successful
- # execution date of a task instance):
- # SELECT start_date FROM task_instance WHERE dag_id = 'xx' AND task_id = 'yy' AND state = 'success'
- # ORDER BY start_date DESC NULLS LAST LIMIT 1;
- # Existing "ti_state_lkp" is not enough for such query when this table has millions of rows, since
- # rows have to be fetched in order to retrieve the start_date column. With this index, INDEX ONLY SCAN
- # is performed and that query runs within milliseconds.
Index("ti_pool", pool, state, priority_weight),
Index("ti_job_id", job_id),
Index("ti_trigger_id", trigger_id),
