Move requires_grad_/backward out of VariableTypeManual. (#54543)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/54543
Test Plan: Imported from OSS
Reviewed By: eellison
Differential Revision: D27321819
Pulled By: ailzhang
fbshipit-source-id: 991c83e134d109e270c872b4b79026dcb732d77a
