[caffe2] allow dropout to take 1.0 as dropout ratio to zero-out a layer (#72741)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/72741
as titled.
Context:
This is useful in fast mitigating feature induced overfitting in the sense that we can do omni-transfer on a trained model and apply dropout with ratio = 1 on features resulting in overfitting. Directly removing the features would not be feasible on omni-transfer scenarios since the downstream FC sizes would change.
Experimental records:
https://fb.quip.com/npIkAgRc8jl9#temp:C:DWC050ceaba14424d23a78462c01
Doing dropout = 1 on selected features improves the eval NE over the next few hours (compared to v0 baseline) as is shown in the figures.
Test Plan:
```
buck test caffe2/caffe2/python/operator_test:dropout_op_test
```
Reviewed By: ustctf
Differential Revision: D34178732
fbshipit-source-id: 533feebe21bc582eefd756de397d5c7807c7438d
(cherry picked from commit 5dabf9c484c0bc5410e3700e3010cdabb4bf903c)
