Revert Cookie2 added to list

[hamishwillee]

Remove Cookie2 from a list, reverting its addition in #41830

The Cookie2 was originally removed in #13965 because the header is not supported by any browser - where supported means "the browser actually does something to include it", not that it can be included by servers etc.
While we'd happily include something that has no browser integration, we don't include headers that are obsoleted and have no browser integration, because they are no longer considered part of the web platform,

[github-actions]

Preview URLs

• /en-US/docs/Glossary/Forbidden_request_header

Flaws (1)

URL: /en-US/docs/Glossary/Forbidden_request_header
Title: Forbidden request header
Flaw count: 1

• macros:
  • Can't resolve /en-US/docs/Web/HTTP/Reference/Methods/TRACK

External URLs (2)

URL: /en-US/docs/Glossary/Forbidden_request_header
Title: Forbidden request header

• https://crbug.com/571722 (1 time)
• https://fetch.spec.whatwg.org/ (1 time)

[estelle]

Thanks! 🎉