Removed force_i18n in API v2 settings serializer

refs TryGhost#10582

- deprecated
- won't serve
- won't save

core/server/api/v2/utils/serializers/input/settings.js

@@ -48,5 +48,12 @@ module.exports = {
                 setting = url.forSetting(setting);
             }
         });
+
+        // CASE: deprecated, won't accept
+        const index = _.findIndex(frame.data.settings, {key: 'force_i18n'});
+
+        if (index !== -1) {
+            frame.data.settings.splice(index, 1);
+        }
     }
 };