ns for fx: clean up override_qengines and copy TODO in tests (#61358)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61358
1. changes override_qengines to require fbgemm instead, these
tests are not testing any qengine specific logic so better to just
run them once
2. removes a TODO about copy.deepcopy which we do not plan to address
Test Plan:
```
python test/test_quantization.py TestFXNumericSuiteCoreAPIs
```
Imported from OSS
Reviewed By: hx89
Differential Revision: D29600352
fbshipit-source-id: 4db08f0080233ff46d7679928c83e41c5ba21ec8
