Arm backend: Remove unused c++ using in arm_executor_runner.cpp

[zingo]

cc @digantdesai @freddan80 @per @oscarandersson8218

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13217

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❌ 1 New Failure, 1 Cancelled Job, 1 Unrelated Failure

As of commit 280ed16 with merge base 2798b6c ():

NEW FAILURE - The following job has failed:

• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 9fa9943827995767f7886f2f3ae8b9322ad3c87daf37452674d6e05d0ed5d72d /exec failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• trunk / test-models-macos-coreml (dl3) / macos-job (gh)
  ##[error]The operation was canceled.

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

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

• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'quantized_decomposed' object has no attribute 'convert_element_type'

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[zingo]

test fails are unrelated