Remove deprecated XNNPACK capture utilities and migrate tests (#18134)

[JacobSzwejbka]

Summary:

Delete capture_graph_for_xnnpack() and get_xnnpack_capture_config() which
were only used in test files and relied on the deprecated exir.capture API.
Migrate test_xnnpack_utils.py to use inline to_edge(export(...)) calls.
Remove the deprecated exports from xnnpack/init.py.

Differential Revision: D95605468

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18134

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❌ 2 New Failures, 6 Pending, 2 Unrelated Failures

As of commit 0076b99 with merge base 8c32dc8 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / macos / macos-job (gh)
  backends/xnnpack/test/ops/test_conv2d.py::TestConv2d::test_qs8_conv2d_bn
• pull / unittest-arm-backend-with-no-deps (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 4b7417d4c4825f1bd7ca61fc9adfb720a31e943c4145ed6d82c9f14645fe7d4d /exec failed with exit code 1

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / test-eval_llama-wikitext-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-lora-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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[meta-codesync]

@JacobSzwejbka has exported this pull request. If you are a Meta employee, you can view the originating Diff in D95605468.

[github-actions]

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[digantdesai]

Looks OK to me. @GregoryComer can you take a look as well?