fix(signin): pass account data to broker instead of using currentUser

@shane-tomlinson feedback appreciated!
This seems like another bug. If you log in using cached Sync credentials, we weren't actually forwarding the session token to `onSignInSuccess` because `recoveryEmailStatus ` doesn't return one, so the oauth flow should break. This is caught by the new functional test, but maybe we should add an explicit/reduced test case for this.