Remove Link Autofill

[annemirasol]

Fixes #3612

Changes proposed in this Pull Request:

Removes Link Autofill Modal, as part of the move to Link in the Payment Element.

Testing instructions

Objective: Test that Link autofill is no longer present, and nothing broke from the checkout process.

1. Enable Link as a payment method.
2. As a logged in shopper, add a product to cart and go to block checkout.
3. For logged in shoppers, we expect the email address field to be pre-filled. Verify that the Link button is no longer there.
4. Verify that you can finish purchasing your order without any problem.
5. Repeat steps 2-5 for shortcode checkout.

Notes

• With us no longer passing the Link autofill beta flag, if Link is enabled as a payment method, customers should see Link in their Payment Element. This is expected. Improvements to end-to-end experience will be addressed in a separate work.

User is signed out	User is signed out (expanded)	Prompt to sign up

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• Covered with tests (or have a good reason not to test in description ☝️)
• Added changelog entry in both changelog.txt and readme.txt (or does not apply)
• Tested on mobile (or does not apply)

Post merge

• Added testing instructions to the Release Testing Instructions wiki page (or does not apply)
• Added the needs docs label (or does not apply)
• Included this PR in the Release Thread scope (or does not apply)

[wjrosa]

Code is good and it works as it should: