Updated the middleware api docs env section to remove dev and prod (v…

…ercel#36739)

…rding due to customer confusion

This PR updates the middleware (edge functions) api docs environment section to remove the dev and prod wording due to customer confusion

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

docs/api-reference/edge-runtime.md

@@ -26,7 +26,7 @@ The Next.js Edge Runtime is based on standard Web APIs, which is used by [Middle
 
 ### Environment
 
-- `process.env`: Holds an object with all environment variables for both production and development in the exact same way as any other page or API in Next.js
+- `process.env`: Holds an object with all environment variables for both `next dev` and `next build` in the exact same way as any other page or API in Next.js
 
 ### Fetch