Retire Node Eligibility Service (NES) [Closing Down]

### Value Prop
GitHub Enterprise Server is removing an unused service, Node Eligibility Service (NES), to keep the platform lean and well-maintained. This cleanup reduces unnecessary complexity in your self-hosted environment without affecting any customer-facing functionality.

### Expected Outcome
Retiring this service eliminates dead code and maintenance burden that provided no customer value.

路线图 issue 提到了 Node Eligibility Service (NES)，但没有提供 repository 文件、测试或入口点。首先在 GitHub Enterprise Server 代码库中定位 NES，并确认其归属和依赖项；当这个未使用的服务在不影响客户的情况下被移除后，即视为完成。

由索引模型根据 Issue 内容生成。