Remove _finfo; replace _finfo usage with torch.finfo (#15165)
Summary:
This PR removes the usage of _finfo defined in torch.distributions.utils and changes the call sites
to use torch.finfo instead
Differential Revision: D13451936
Pulled By: soumith
fbshipit-source-id: 6dbda3a6179d9407bc3396bf1a2baf3e85bc4cf2
