Drop old quantization flows

[namgyu-youn]

Summary:
This PR drops old quantization flows:

torchao/quantization/subclass.py
torchao/quantization/weight_only.py
torchao/quantization/dynamic_quant.py

Applies corresponding change in other parts for removing old quantization flows:

torchao/quantization/quant_api.py
torchao/quantization/utils.py
torchao/quantization/autoquant.py

# Remove old test cases
test/integration/test_integration.py

# SmoothQuant with old workflow is dropped
# Use torchao/prototype/smoothquant instead with new api
torchao/quantization/smoothquant.py

• fix: Deprecate and remove subclass.py, dynamic_quant.py, and weight_only.py #2745

Test plan: test/integration/test_integration.py

[pytorch-bot]

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[namgyu-youn]

How about inlining _int8wo_api, _int8da_int8w_api, _int4wo_api ? They are used only once across codebase.

[namgyu-youn]

Temporarily updated to use new APIs 2 times to fix CI, but maybe we can update _bench_quantized_tensor_subclass_perf to compare only original vs. new quantization flows?