You could edit the file and paste it in, but I was thinking about creating a plugin. You go to Plugins & Products > Add New Plugin, paste that code in the big box, select the hook location (either cron_script_cleanup_daily or cron_script_cleanup_hourly), enter a title (something so that you'll remember what it is in the future), check "Yes" to make it active. The other fields you can leave as default. Then press "Save" when you're done.
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