Jetpack Forms: remove links from the response emails sent to site owners

[donnchawp]

As site owners reply to form responses to contact their customers, they didn't want links to wp-admin in the email. This PR removes the two links in a backwards compatible way, in case any customer has decided to modify the template already.

Proposed changes:

• Remove the view response and edit links from the form response emails.
• Leave in the %3$s and %4$s arguments in case any site owner has changed the template already.

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

pcsBup-yo-p2#comment-497

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

No

Testing instructions:

Apply PR.
Embed a contact form in a test post.
Fill in the form.
You should receive an email with the form response. It will not link to the feedback admin page, or to the post editor.

Before and after screenshots:

[github-actions]

Thank you for your PR!

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

• ✅ Include a description of your PR changes.
  
• ✅ All commits were linted before commit.
  
• ✅ Add a "[Status]" label (In Progress, Needs Team Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

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 🤖

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The e2e test report can be found here. Please note that it can take a few minutes after the e2e tests checks are complete for the report to be available.

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Once your PR is ready for review, check one last time that all required checks (other than "Required review") appearing at the bottom of this PR are passing or skipped.
Then, add the "[Status] Needs Team Review" label and ask someone from your team review the code. Once reviewed, it can then be merged.
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[github-actions]

Are you an Automattician? You can now test your Pull Request on WordPress.com. On your sandbox, run

bin/jetpack-downloader test jetpack update/remove_links_from_forms_email

to get started. More details: p9dueE-5Nn-p2

[CGastrell]

Worked fine for me!