Remove osft_output_dtype #36
Description
This was added initially when directly working with OSFT. However; since integrating OSFT into mini trainer and working through the various mixed-precision training issues, output_dtype now gets in the way more than it is useful, so it would be best if we can drop it entirely and use the existing other dtypes such as osft_upcast_dtype, save_dtype, and the new train_dtype being introduced in #32.