clean up the TracingState API (#21564)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21564
ghimport-source-id: b6f71e2238f6f7c8de6cfbf6969a5e08e07be46c
Reviewed By: suo
Differential Revision: D15729497
Pulled By: zdevito
fbshipit-source-id: aacfea6058fadb572df692aa9ebd6cab0bcd03fc
