Revert "Fixed private mode cookie for local development (TryGhost#17938…

…)" (TryGhost#19298)

This reverts commit f303eee.

refs https://ghost.slack.com/archives/C0568LN2CGJ/p1702277420152709
https://linear.app/tryghost/issue/PROD-46/rss-url-for-private-mode-site-is-hardcoded

ghost/core/core/frontend/apps/private-blogging/lib/middleware.js

@@ -55,8 +55,7 @@ const privateBlogging = {
  name: 'ghost-private',
  maxAge: constants.ONE_MONTH_MS,
  signed: false,
- sameSite: urlUtils.isSSL(config.get('url')) ? 'none' : 'lax',
- secure: urlUtils.isSSL(config.get('url'))
+ sameSite: 'none'
  })(req, res, next);
  },