Fix SinglePositionMultiTokenCandidateGenerator signature (#49413)
`input_ids` and `model_kwargs` were dropped from the call site in #48982 and
marked as deprecated, but they are still declared as required positional
parameters, so building the generator raises a `TypeError`. `@deprecate_kwarg`
only emits a warning, it does not supply a default.
Both arguments are unused in the body, so give them a default and move them
after the required ones, in line with the other candidate generators.