[FSDP][StateDict] Allow FULL_STATE_DICT option for 2D (#120837)
Fixes #120722
TL;DR for the issue:
As users are expected to use get_model_state_dict to do state_dict retrieval, I think it's fine to remove the warning and RuntimeError.
More context in #120722.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120837
Approved by: https://github.com/Skylion007
