[Quant] Remove explicitly default QConfigMapping settings (#90066)
Summary: Previously we explicitly set a qconfig for ops
like conv and linear in the default QConfigMapping. However,
this makes it difficult for user to override the global and
have the new global take effect for basic ops. This commit
removes these explicit settings so the user can simply run
the following to quantize these ops.
```
qconfig_mapping = get_default_qconfig_mapping()
qconfig_mapping.set_global(my_qconfig)
```
There is no change in behavior for the default use case
of not setting anything on the default QConfigMapping.
Test Plan:
python test/test_quantization.py TestQuantizeFx.test_default_qconfig_mapping_override_global
Reviewers: vkuzo, jerryzh168
Subscribers: vkuzo, jerryzh168
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90066
Approved by: https://github.com/vkuzo, https://github.com/jerryzh168