Hi Deyson,
s2Member’s transient options are created through the WordPress function set_transient() in s2Member’s IPN/PDT functionality. As it’s name suggests this data lasts only for a short time; WordPress automatically deletes this data after a while.
If you’re running a live site, this transient data is very important, as it is vital for finding if transactional data has been processed before. When you see Not processing. Duplicate IPN within s2Member’s logs, this is because s2Member picks up that it has processed this transaction before because it is stored within transient data.
So, to answer your question, no. It would be unwise to delete transient data of any kind (especially s2Member’s IPN transient data), as it is important for the time that it is there, and when it’s not needed WordPress will delete the data automatically.
If you’d like to check out the source code that deals with transient data, you can look in the files within s2member/includes/classes/ that start with paypal-notify-in-. You can check it out within your WordPress setup or in the Codex.