[Settings] Remove SMS preference setting

[YodaLightsabr]

Remove this setting:

Our new authentication flow relies on the last successful login preference, not the "Prefer login codes via SMS" setting. It might be worth dropping the column, too.

[Luke-Oldenburg]

I may be misunderstanding but it appears from the code that this toggle is used to determine whether SMS auth is available at all. Maybe it's labeled wrong?