Fix protobuf warnings in caffe2 (#56186)
Summary:
This guards some deprecated usages of the Protobuf API behind an `#ifdef` (this is how onnx does it as well)
](https://our.intern.facebook.com/intern/diff/27803121/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56186
Pulled By: driazati
Reviewed By: bertmaher, dzhulgakov
Differential Revision: D27803121
fbshipit-source-id: 2d3a348ec1ab9879a0d8f2dff17c5444fd4baf2c
Author
davidriazati@fb.com
