Cleaning et_schema of InferenceRun for OSS (#565)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/565

These are concepts that aren't useful in the OSS world. Associated tests were also moved

- Moved out InferenceRun, OperatorGraphWithStats, ExportedETOperatorGraph for internal
- Changed FXOperatorGraph to extending OperatorGraph instead of OperatorGraphWithStats
- Tests for EDIR (to be renamed) moved to internal since they are heavily coupled with InferenceRun

Reviewed By: tarun292

Differential Revision: D49839120

fbshipit-source-id: f20ba1f88f8461125b3bfd3f487c8f91d8169d7e