Remove qconfig_dict in top level eager mode quantization API (#31972)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31972
Since eager mode quantization requires many user modifications, we can't
consistently quantize a given model by just changing qconfig_dict, therefore
the top level `qconfig_dict` is not that useful.
fixes: https://github.com/pytorch/pytorch/issues/31549
Test Plan:
.
Imported from OSS
Differential Revision: D19330691
fbshipit-source-id: 8aee6e5249e0c14e8a363ac1a83836e88887cd7d
