Ok I looked around and wrote this up. This should cover every way you added Audit Defense.
You get Audit Defense when you purchase PLUS Help & Support, MAX Defend & Restore, or Premium Services for Turbo Tax Online or Audit Defense for Turbo Tax CD/download
https://ttlc.intuit.com/community/choosing-a-product/help/which-returns-are-eligible-for-audit-defen...
So to remove Audit Defense you need to remove Plus or MAX or Premium Services,
Remove MAX
https://ttlc.intuit.com/community/downgrading/help/can-i-remove-max/00/26691
Remove PLUS Benefits
https://ttlc.intuit.com/community/downgrading/help/can-i-remove-plus-benefits-before-i-pay/00/26429
Remove Premium Services with Audit Defense for California filers
https://ttlc.intuit.com/community/downgrading/help/how-do-i-remove-premium-services/00/26266
