NXP backend: Remove optimization in prune_cast_operators.py

[roman-janik-nxp]

Summary

Remove unnecessary optimization in prune_cast_operators.py in IR optimizer.

Test plan

All tests where a subgraph is delegated to Neutron.

cc @digantdesai @JakeStevens @robert-kalmar @Pop-korn

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13377

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✅ You can merge normally! (4 Unrelated Failures)

As of commit 627f084 with merge base ea4a7fa ():

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

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

• pull / unittest / linux / linux-job (gh) (trunk failure)
  examples/models/llama/tests/test_ring_attention.py::TestRingAttention::test_single_token_processing_quantized
• pull / unittest / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-editable / linux / linux-job (gh) (trunk failure)
  examples/models/llama/tests/test_ring_attention.py::TestRingAttention::test_single_token_processing_quantized
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[roman-janik-nxp]

@pytorchbot label "module: nxp" "release notes: nxp"

[MartinPavella]

LGTM