[Quant][fx][bc-breaking] Remove unused functions in fx/utils.py (#90025)
Summary and BC-breaking notes: This commit removes the following
unused functions from both the `torch.quantization` and the
`torch.ao.quantization` namespaces:
```
graph_pretty_str
get_per_tensor_qparams
quantize_node
get_qconv_op
create_qparam_nodes
node_return_type_is_int
is_get_tensor_info_node
```
Test Plan:
python test/test_quantization.py TestQuantizeFx
python test/test_quantization.py TestQuantizeFxOps
python test/test_quantization.py TestAOMigrationQuantizationFx
Reviewers: jerryzh168, vkuzo
Subscribers: jerryzh168, vkuzo
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90025
Approved by: https://github.com/HDCharles
