Remove privacy sandbox content from 3rd-party cookies guide

[chrisdavidmills]

Description

With Google's privacy sandbox suite of technologies largely being de-decommissioned (see https://privacysandbox.com/news/update-on-plans-for-privacy-sandbox-technologies/), it makes sense to start removing MDN's coverage of it, and marking impacted features as deprecated.

This PR updates our Third-party cookie guide to remove any mention of the privacy sandbox and impacted features. Note that private state tokens are standardized and are being kept.

Motivation

Additional details

Related issues and pull requests

Fixes #41778

[github-actions]

Preview URLs

• /en-US/docs/Web/Privacy/Guides/Third-party_cookies
• /en-US/docs/Web/Privacy
• /en-US/docs/Web/Security

Flaws (3)

Note! 2 documents with no flaws that don't need to be listed. 🎉

URL: /en-US/docs/Web/Security
Title: Security on the web
Flaw count: 3

• unknown:
  • No generic content config found
  • no blog root
  • no blog root

External URLs (4)

URL: /en-US/docs/Web/Privacy/Guides/Third-party_cookies
Title: Third-party cookies

• https://learn.microsoft.com/en-us/microsoft-edge/web-platform/tracking-prevention (1 time) (Note! This may be a new URL 👀)
• https://privacysandbox.google.com/protections/private-state-tokens (1 time) (Note! This may be a new URL 👀)
• https://webkit.org/tracking-prevention-policy/ (1 time) (Note! This may be a new URL 👀)
• https://webkit.org/tracking-prevention/ (1 time) (Note! This may be a new URL 👀)