chore(db): drop the job log schedule index the occurrence unique index covers (#9398)

Author: waleedlatif1

packages/db/migrations/0438_drop_redundant_job_log_schedule_index.sql

@@ -0,0 +1,6 @@
+-- job_execution_logs_schedule_occurrence_unique (schedule_id, occurrence_at) leads with
+-- schedule_id, so it serves every lookup and FK check the single-column index did.
+COMMIT;--> statement-breakpoint
+SET lock_timeout = 0;--> statement-breakpoint
+DROP INDEX CONCURRENTLY IF EXISTS "job_execution_logs_schedule_id_idx";--> statement-breakpoint
+SET lock_timeout = '5s';