ns for fx to backend_config_dict [1/x]: fused and qat modules
Summary:
NS for FX mappings were originally hardcoded, because quantization op
mappings were not easily reusable. Now that we have `backend_config_dict`,
we can start moving NS for FX to use them and delete the hardcoded mappings.
This first PR deletes the hardcoded mappings for `nni` and `nniqat` modules,
and instead reads these mappings from `backend_config_dict`.
Future PRs will incrementally move more of the mappings over.
Test plan:
```
python test/test_quantization.py -k FXNumericSuite
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76958
Approved by: https://github.com/jerryzh168
