Fix exception message of `torch.optim.AdamW`. (#36088)
Summary:
PyTorch does not implement `SparseAdamW`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36088
Differential Revision: D20932357
Pulled By: gchanan
fbshipit-source-id: 49e5b72c34ff8ce0deb6b3807662b8b7d67d959f
