No, as of March 25th the ability to unlink accounts from a Bungie profile was disabled (except for Twitch). Even if that change had not happened, you would have still needed the login info to have been able to deactivate cross-save and then subsequently unlink the account. Its also somewhat a good thing in your case that you can't do it, as your characters are permanently bound to your Stadia account which is your active profile, so if you were able to deactivate cross-save and unlink the account you would have lost your characters.