Revert D23494065: Refactor CallbackManager as a nested class of RecordFunction.
Test Plan: revert-hammer
Differential Revision:
D23494065 (https://github.com/pytorch/pytorch/commit/63105fd5b192e2fe9310dd0445d73af79e3880b3)
Original commit changeset: 416d5bf6c942
fbshipit-source-id: 3b1ec928e3db0cc203bb63ec4db3da1584b9b884
