Completing the retirement of the alert system

The alert system had some potential uses but also had issues that made it problematic. It was a frequent source of misunderstanding about the security model and effective governance. Furthermore, the system was not scalable to different software vendors, and no one could tell who created a message. Additionally, there was good reason to believe that the key was compromised. Due to these issues, the alert system has been deactivated, and Gregory Maxwell via Bitcoin-dev plans to send a triggering alert in the future and disclose the private key in public to eliminate any further potential of reputation attacks and diminish the risk of misunderstanding the key as some special trusted source of authority.