[firebase_ui_auth] Delete account should disconnect from the user's social authentication

[kwill39]

Currently, the Delete account button deletes the user from Firebase Auth, but it doesn't disconnect from their social authentication. For example, if someone uses Sign in with Google, their Google account will be connected with the app. If the user then deletes their account using the Delete account button, their account will be deleted from Firebase Auth, and they'll be signed out of the app, but their Google account will still show a connection with the app under "Apps with access to your account". See Signing Out and Disconnecting Accounts for a better understanding of what I'm referring to.