Remove duplicate rows

synapse/storage/schema/delta/16/remove_duplicates.sql

+
+
+DELETE FROM event_to_state_groups WHERE state_group not in (
+    SELECT MAX(state_group) FROM event_to_state_groups GROUP BY event_id
+);
+
+DELETE FROM event_to_state_groups WHERE rowid not in (
+    SELECT MIN(rowid) FROM event_to_state_groups GROUP BY event_id
+);