This argument was added with the default incorrectly set to `True` in
bb0eb76bf3 - despite
`maybe_send_to_registration` only ever being called in production code
in a single place, with `password_required=False` explicitly. And then
it just got carried forward through refactors.
`maybe_send_to_registration` was/is also called twice in tests, falling
back to the default, but the `password_required` value is irrelevant to
the tests - and if anything letting it use the `True` has been wrong,
due to not matching how this function is actually used.
3ed2a30e01