Clarify when softplus is reverted to linear. (#32945)
Summary:
The default value is removed because it is explained right below.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/32945
Reviewed By: soumith
Differential Revision: D19706567
Pulled By: ailzhang
fbshipit-source-id: 1b7cc87991532f69b81aaae2451d944f70dda427
