fix: Correct variables used in errors in sign.js

I couldn't figure out how to get a name for the no_suitable_app error
unfortunately, so that's just commented out.

/puter/packages/backend/src/routers/sign.js
   65:74  error  'subject' is not defined  no-undef
  114:59  error  'subject' is not defined  no-undef

packages/backend/src/routers/sign.js

@@ -62,7 +62,8 @@ module.exports = eggspress('/sign', {
 
         app = await get_app({ uid: req.body.app_uid });
         if ( ! app ) {
-            throw APIError.create('no_suitable_app', null, { entry_name: subject.entry.name });
+            // FIXME: subject.entry.name isn't available here
+            throw APIError.create('no_suitable_app', null); //, { entry_name: subject.entry.name });
         }
         // Generate user-app token
         const svc_auth = Context.get('services').get('auth');
@@ -111,7 +112,7 @@ module.exports = eggspress('/sign', {
 
         const svc_acl = Context.get('services').get('acl');
         if ( ! await svc_acl.check(actor, node, 'see') ) {
-            throw await svc_acl.get_safe_acl_error(actor, subject, 'see');
+            throw await svc_acl.get_safe_acl_error(actor, node, 'see');
         }
 
         if ( app !== null ) {