Arm backend: Remove silu decomposition pass

[AdrianLundell]

Instead handle silu similar to other table op activations

cc @freddan80 @per @zingo @oscarandersson8218 @digantdesai

[pytorch-bot]

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❌ 6 New Failures

As of commit 0c9e364 with merge base 3b819a2 ():

NEW FAILURES - The following jobs have failed:

• pull / test-samsung-models-linux / linux-job (gh)
  RuntimeError: Command docker exec -t c30dc42888f1c2926798beafbed5bdeb135c7b6c3a785edc05eb3d540df63d45 /exec failed with exit code 1
• pull / test-samsung-quantmodels-linux / linux-job (gh)
  RuntimeError: Command docker exec -t 3502a27da7a8a79e62c17ceede409a5386b6e1ceef266797736de58b65e5be50 /exec failed with exit code 1
• pull / unittest / macos / macos-job (gh)
  examples/models/test/test_export.py::ExportTest::test_mv3_export_to_executorch
• pull / unittest-editable / linux / linux-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_dq_conv2d_seq
• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model
• trunk / test-mcu-cortex-m-backend / linux-job (gh)
  RuntimeError: Command docker exec -t ddfe38c7ac5369e66390fbee10597d062f1a6d166d1e7a5f22c2636fe4457590 /exec failed with exit code 1

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[zingo]

Approved BUT if possible please wait to after #17200 is merged and rebase before merging (if rest is green) to prove Arm tests PASS.

[zingo]

Merged now, I will rebase to test.