fix: align group management APIs

server/db/mysql/schema.sql

@@ -13,7 +13,7 @@
 #
 # - Default tenant business database: tinode
 #   - im_users, im_topics, im_subscriptions, im_messages and extension tables
-#   - im_http_idempotency and im_business_events_outbox for reliable HTTP writes
+#   - im_http_idempotency for HTTP write idempotency
 #   - im_file_review_tasks for asynchronous content safety and malware checks
 #   - business tables do not store tenant_id in independent-database mode
 #