Update using-executorch-export docs

[lucylq]

1. Remove unused partial_function
2. Add import torch
3. Add pybindings example for program-data separation

pick to 1.0 release

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/14552

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 3 New Failures, 2 Unrelated Failures

As of commit 2f5b6e2 with merge base b3f3111 ():

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-wheel-packages-linux (3.10) / linux-job (gh)
  RuntimeError: Command docker exec -t 35dcaf9d770240c70cc6bb5a6fda3ea421d8f75eb1a42c26aff35371cc69eef7 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.11) / linux-job (gh)
  RuntimeError: Command docker exec -t 250201a4e55304dd7a44af0658534dc46ce825c46eca712c5bec31e8f7351e16 /exec failed with exit code 1
• pull / test-qnn-wheel-packages-linux (3.12) / linux-job (gh)
  RuntimeError: Command docker exec -t b3a16dd3fd9d421c750299cac2129faba16845b956e02c3c406c732ec1d89cdd /exec failed with exit code 1

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• pull / test-binary-size-linux-gcc / linux-job (gh) (similar failure)
  ##[error]The operation was canceled.

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

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

• pull / test-setup-linux-gcc / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[lucylq]

@pytorchbot cherry-pick --onto release/1.0 -c docs

[pytorchbot]

Cherry picking #14552

The cherry pick PR is at #14598 The following tracker issues are updated:

• [v1.0.0] Release Tracker #14288 (comment)

Details for Dev Infra team

Raised by workflow job