Revert "FEATURE: Add same site cookie 'None' option to make cross domain systems possible (#9374)"

samesite=none is not supported in Rack 2.0.8. We can re-apply this change once Rack has been upgraded.

https://meta.discourse.org/t/cooke-samesite-none-not-working-because-of-outdated-rack-version/151331

This reverts commit 94c0228681.

config/site_settings.yml

@@ -1382,8 +1382,7 @@ security:
       - Lax
       - Strict
       - Disabled
-      - None
-    regex: "^(Lax|Strict|Disabled|None)$"
+    regex: "^(Lax|Strict|Disabled)$"
   enable_escaped_fragments: true
   allow_index_in_robots_txt: true
   moderators_create_categories: false