Remove deprecated graph mode quantization tests (#24998)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/24998
Original graph mode was developed at the time when we don't have conrete API of qconfig yet and
it has a global observer module which is passed around during the whole quantization flow,
we have a much clearer picture of quantization API now, and we are going to use a per Tensor
observer design, just like in eager mode. This PR removes the deprecated tests, next PR will
remove deprecated code.
Test Plan:
```
python test/test_quantizer.py
```
Imported from OSS
Differential Revision: D17001140
fbshipit-source-id: 87f342cfa8ea6b45606372c51dbfc493065a737a
