Hi,
So by the looks of it, you removed the fields in the database, but you haven't updated the MYSQL query in your application, where you build the MYSQL query in PHP you must remove references to pg_paypal_pro_api_username and pg_paypal_pro_api_password and pg_paypal_pro_api_signature
If any decent IDE you can do find in files and just search for the keyword pg_paypal_pro_api_username - that will take you to where the MYSQL query is being built.
If it produces a different error let me know - as it may just be a bit of editing gone wrong.
If in the query looks like
pg_paypal_pro_api_username = '', pg_paypal_pro_api_password = '', pg_paypal_pro_api_signature = '',
you must remove all of that
If it works please accept my bid