Remove mixed precision hook as part of the unwrap_model (#860)
* Mixed precision hook
* Rename
* Rm comment, need to move
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
* Fix doc
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>