[PG Wrapper][BE] Make some methods private (#66166)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66166
These methods should be private.
ghstack-source-id: 139782587
Test Plan: CI
Reviewed By: cbalioglu
Differential Revision: D31353020
fbshipit-source-id: 583fb315cc2cacc37df3d29cd5793b42558930b3
