In correct error message when Passwordless SMS is enabled but to disable it

`Can't save the config. At least one authenticator for type email is needed.`

Step to reproduct, at staging server:
1. Setup: Enabled Passwordless for SMS, Phone No
2. Action: Disable Phone No, Enable Email as Login ID

Show the above error message, which is not relevant; The correct course of action is to disable Passwordless for SMS, and step 2 is okay now.


Start by reproducing the staging configuration flow: enable Passwordless for SMS and phone number, then disable phone number and enable email as the login ID. Trace the configuration save validation that produces the email-authenticator error; done means this combination no longer shows the irrelevant message and the reported Passwordless setting guidance is correct.

Written by the indexing model from the issue text.