reference index - env vars and headers no longer in reference section

reference/index.html.md

@@ -40,9 +40,6 @@ An explanation of how Fly.io's proxy distributes traffic to your application ins
 * [**Monorepo and Multi-Environment Deployments**](/docs/reference/monorepo/):
 The command options you can use with flyctl to build and deploy multiple apps from a monorepo or deploy an app to multiple targets.
 
-* [**Runtime Environment**](/docs/machines/runtime-environment/):
-The environment variables that are set when an App runs on Fly.io and the request headers which provide Apps with information about incoming connections.
-
 * [**Secrets - Build time**](/docs/reference/build-secrets/):
 How to set and use Docker secrets to make secrets available at build time.