ns for fx: remove duplicated BNReLU mappings
Summary:
These mappings are already defined for `BatchNorm{n}d` as the root
node, we don't need to specify them again. Removing to clean
up the code.
Test plan:
```
python test/test_quantization.py -k FXNumericSuite
python test/test_quantization.py -k FXGraphMatcher
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/76993
Approved by: https://github.com/jerryzh168
