Remove contact form legacy admin files

[CGastrell]

WIP - Only after menu item is fully deprecated

Part of FORMS-132

Proposed changes:

Remove now unused files

Other information:

• [ ] Have you written new tests for your changes, if applicable?
• [ ] Have you checked the E2E test CI results, and verified that your changes do not break them?
• [ ] Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

No

Testing instructions:

TBD

[github-actions[bot]]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the remove/contact-form-legacy-admin-files branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack remove/contact-form-legacy-admin-files

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions[bot]]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation :robot:

---

Follow this PR Review Process:

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[jp-launch-control[bot]]

Code Coverage Summary

Coverage changed in 2 files.

File	Coverage	Δ%	Δ Uncovered
projects/packages/forms/src/contact-form/class-editor-view.php	0/156 (0.00%)	0.00%	-1 💚
projects/packages/forms/src/contact-form/class-util.php	33/175 (18.86%)	0.21%	-2 💚

Full summary · PHP report · JS report

_{Coverage check overridden by https://github.com/Automattic/jetpack/labels/Coverage%20tests%20to%20be%20added%20later.}

[github-actions[bot]]

This PR has been marked as stale. This happened because:

• It has been inactive for the past 3 months.
• It hasn't been labeled `[Pri] BLOCKER`, `[Pri] High`, `[Status] Keep Open`, etc.

If this PR is still useful, please do a [trunk merge or rebase](https://github.com/Automattic/jetpack/blob/trunk/docs/git-workflow.md#keeping-your-branch-up-to-date) and otherwise make sure it's up to date and has clear testing instructions. You may also want to ping possible reviewers in case they've forgotten about it. Please close this PR if you think it's not valid anymore — if you do, please add a brief explanation.

If the PR is not updated (or at least commented on) in another month, it will be automatically closed.