CHEF-25757 - standardize - remove_sla_from_readme

[cgunasree08]

This pull request removes the oft-misleading Chef SLA text from the README.md file.

This action is being taken as part of the 2025 Repo Standardization Initiative. As Progress Chef makes a best effort to respond to issues and pull requests in a timely manner, and prioritizes bugfixes and security updates on a customer-driven basis (which may span repos, or have no repo footprint at all), we no longer support the concept of a Service Level Agreement (SLA) on a repository-centric basis. For further details, see Repo SLA Removal FAQ.