Remove deprecated codepath for old-style autograd.Function (#30696) (#33956)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/33956
Test Plan: Imported from OSS
Differential Revision: D20167359
Pulled By: glaringlee
fbshipit-source-id: 9b323bd29eca97bce0475225ad2b3b2ded29005d
