Remove Unstable-only features from 2.15 spec

Removes features that should only be in Unstable:
- /macros and /macros/{macro_id} endpoints
- /conversations/{conversation_id}/handling_events endpoint
- /messages/status endpoint
- macro, macro_list, handling_event, handling_event_list schemas
- Macros tag

These features were inadvertently included when 2.15 was derived from
Unstable. Features already in 2.14 (sms_message, whatsapp) are retained.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: markdennis22