[DataPipe] removing unbatch_level from .groupby (#70249)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70249
IMO, the `unbatch_level` argument is not needed here since users can simply can `.unbatch` before calling `.groupby` if needed. One small step closer to an unified API with other libraries.
Note that we may rename the functional name from `.groupby` to `.group` in the future. TBD.
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D33259104
Pulled By: NivekT
fbshipit-source-id: 490e3b6f5927f9ebe8772d5a5e4fbabe9665dfdf
