chore: trim migration comments

Signed-off-by: anilb <epipav@gmail.com>

Author: epipav

backend/src/osspckgs/migrations/V1784745489__sequin_backfill_sort_column_indexes.sql

@@ -1,9 +1,3 @@
--- Sequin backfills paginate with a keyset cursor of (sort column, primary key),
--- e.g. WHERE ("last_synced_at", "id", "package_id") >= ($1, $2, $3) ORDER BY ... LIMIT n.
--- Without these indexes every page is a full sort (28M+ rows on versions,
--- 44M+ on package_dependencies) and hits Sequin's per-query timeout.
--- CONCURRENTLY relies on flyway's -mixed=true to run outside a transaction.
-
 CREATE INDEX CONCURRENTLY IF NOT EXISTS versions_last_synced_at_id_package_id_idx
   ON versions (last_synced_at, id, package_id);