Revert "Arm backend: Use FP64 conv in NSS quantized ref"

[zingo]

Reverts #23259

cc @digantdesai @freddan80 @per @oscarandersson8218 @mansnils @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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❌ 1 New Failure, 1 Pending, 2 Unrelated Failures

As of commit 4844319 with merge base 9234be6 ():

NEW FAILURE - The following job has failed:

• Windows MSVC Build / build-windows-arm64 (gh)

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

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

• pull / test-arm-backend-no-driver (test_pytest_models_tosa) / linux-job (gh) (trunk failure)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1
• trunk / test-arm-backend-vkml (test_pytest_models_vkml) / linux-job (gh) (trunk failure)
  RuntimeError: Command bash /__w/_temp/exec_script failed with exit code 1

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