Removed Self-hosted preview of Retool Agents

Retool Agents is currently in public beta on Retool Cloud.

Retool removed the preview release of Agents for self-hosted organizations since Agents is now in public beta with the 3.234.0 edge release and it will be available in the upcoming Q3 stable release. This preview release was intended for deployment into a non-production environment, and was created as a mechanism to allow Self-hosted organizations the opportunity to create agents prior to their availability in an edge or stable release.