Comment form requires WordPress.com login for email address even after account has been closed/purged on simple sites

### Impacted plugin

Jetpack

### Quick summary

When a user attempts to submit a comment using an email address that is no longer associated with a WordPress.com account, but was previously, they are prompted to log in to WordPress.com rather than have the comment submitted.

### Steps to reproduce

Use an email address that was used for a WordPress.com account that has since been closed and purged from the system. See example in p1736874041061979-slack-C029E4HPT

1. Visit a post on a public simple site with comments enabled (and no requirement to log in prior to commenting in Discussion settings)
2. Use the email address from a closed/purged WordPress.com account in the comment form field
3. Submit the comment
4. Prompt will appear to log in to WordPress.com rather than the comment being submmitted

Reported in 9270987-zd-a8c

### Site owner impact

More than 60% of the total website/platform users

### Severity

Minor

### What other impact(s) does this issue have?

No revenue impact

### If a workaround is available, please outline it here.

Commentor must use a different email to make a comment.

### Platform (Simple and/or Atomic)

Simple

Start at the Jetpack comment form on a public Simple site and reproduce the login prompt with an email address from a closed and purged WordPress.com account. Trace the authentication decision for that email; done means the comment submits without requiring a WordPress.com login when the site does not require login.

Written by the indexing model from the issue text.