Remove custom bank account flow

[calvind-stripe]

now that disable_stripe_user_authentication is GA - remove the custom bank account form and the redirect to it at the end of onboarding.

Instead, set disable_stripe_user_authentication to true for Custom accounts and don't specify external_account_collection. Since the latter defaults to true, for Custom accounts we will start collecting bank account info in onboarding without requiring auth.

For all other account types, external_account_collection defaults to true anyways, so bank account info will continue to be collected. And other account types can't disable stripe auth so it's safe to set disable_stripe_user_authentication=false for them.

I tested with custom accounts (to make sure auth is disabled and bank account form is shown) and all other account types (to ensure the POST to v1/account_sessions did not error).

Screen.Recording.2024-10-28.at.5.06.06.PM.mov

Screen.Recording.2024-10-28.at.5.06.06.PM.mov