Revert "Add INT8 SDPA path for CPU"

[jerryzh168]

Reverts #1372

internal bulid error

ao/torchao/csrc/cpu/int8_sdpa.cpp:1:9: error: #pragma once in main file [-Werror,-Wpragma-once-outside-header]
    1 | #pragma once
      |         ^
1 error generated.

[pytorch-bot]

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⏳ 3 Pending, 3 Unrelated Failures

As of commit 880e694 with merge base 10de698 ():

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Run Regression Tests / test (CPU 2.4, linux.4xlarge, torch==2.4.0 --index-url https://download.pytorch.org/whl/cpu, cpu) / linux-job (gh) (trunk failure)
  test/quantization/test_qat.py::TestQAT::test_qat_8da4w_prepare_vs_convert_2
• Run Regression Tests / test (CPU 2.5.1, linux.4xlarge, torch==2.5.1 --index-url https://download.pytorch.org/whl/cpu, cpu) / linux-job (gh) (trunk failure)
  test/quantization/test_qat.py::TestQAT::test_qat_8da4w_prepare_vs_convert_2
• Run Regression Tests / test-nightly (CPU Nightly, linux.4xlarge, --pre torch --index-url https://download.pytorch.org/wh... / linux-job (gh) (trunk failure)
  test/quantization/test_qat.py::TestQAT::test_qat_8da4w_prepare_vs_convert_2

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