Remove callBoxedWorkaround (#36850)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36850
Since now all unboxing happens after dispatch, which means that all c10 ops support unboxing, we can now use op.callBoxed() for all ops and don't need callBoxedWorkaround (which was going through the JIT registry) anymore.
ghstack-source-id: 102879558
Test Plan: waitforsandcastle
Differential Revision: D21102375
fbshipit-source-id: d1e041116563a9650d5a86b07eb96d217d8756f3
