Remove manual database lock usage

src/worker/delete-deprecated-purchases.ts

@@ -1,6 +1,6 @@
 /*
  * server component for the TimeLimit App
- * Copyright (C) 2019 - 2020 Jonas Lochmann
+ * Copyright (C) 2019 - 2021 Jonas Lochmann
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
@@ -53,7 +53,6 @@ async function deleteDeprecatedPurchases ({ database, websocket }: {
       },
       attributes: ['familyId'],
       transaction,
-      lock: Sequelize.Transaction.LOCK.UPDATE,
       limit: 100
     })).map((item) => item.familyId)