To unlink an account from a bungie.net profile the user must prove they own the account by having the proper log in credentials for the account. So to remove the account you will need to log in to bungie.net with your Xbox or Steam credentials. Then click on your account avatar in the top right corner of the website and select Settings. On the Settings screen select Accounts and Linking. Then on that page simply click the red Unlink button next to the PSN account you wish to remove and then enter the log in credentials for that account to confirm removal. If you no long have the PSN credentials then you will need to work with Sony to recover them. Bungie does not have access to user login credentials so they are unable to remove accounts on behalf of players and requiring log in credentials is a security measure to insure ownership of the account which cannot be circumnavigated.