[quant] Remove resnet18 model file, instead fetch from remote (#82447)
### Summary
This PR removes the ResNet-18 model checkpoint and instead fetches the model from remote storage (due to fbcode file size constraints).
### Test Plan:
Run models with: `python test/quantization/core/experimental/fx_graph_mode_apot.py`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82447
Approved by: https://github.com/osalpekar
