When the Membership app is removed from your store, technically, all codes will be automatically removed from your theme. But there are few backlinks which you can remove from the store theme after uninstalling of the application.
1. Go to the Shopify store and click Online Store > Themes > Navigate Actions and Select Edit code.
2. Find aaa_membership in your store theme and delete this backup file from your store for complete installation of the application.
If you want us to have this changes from your store, please feel free to conatct us at firstname.lastname@example.org