Fully deprecate variadic inputs of checkpoint_sequential (#25985)
Summary:
To support variadic inputs of `checkpoint_sequential` was deprecated at https://github.com/pytorch/pytorch/issues/21006. This case should be warned with `DeprecationWarning` for PyTorch 1.2, but it should be simply failed with `TypeError` since PyTorch 1.3. This patch removes the `DeprecationWarning` for PyTorch 1.2.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25985
Differential Revision: D18809875
Pulled By: albanD
fbshipit-source-id: e84dd8629c04979c4b2dc63e8ada94292e8cedd0