refactor: look into deprecating seeded run mode in favor of ensemble-kfold only

[jeffreyHoelzel]

Summary

Currently, seeded run mode is only implemented as a way to handle legacy behavior, but likely is no longer necessary as the user can just one a "single-fold" training run which will do the same thing.

Done when

1. seeded training mode is deprecated.
2. ensemble-kfold can fully mimic single-model functionality.
3. Both modes can be deprecated as we could just pass in the number of folds [1, k) and the corresponding # of seeds.