Update with-universal-configuration example

Feature request

Is your feature request related to a problem? Please describe.

It is confusing for new users to get environment variables set up because there are examples that do not work, and there is an officially supported way of doing environment variables now

https://github.com/zeit/next.js#exposing-configuration-to-the-server--client-side

Describe the solution you’d like

Remove with-universal-configuration from the repo

Describe alternatives you’ve considered

Open to keeping them if someone shows a unique use case.

[timneutkens]

@davcro cool 👍 thanks!

[timneutkens]

It actually serves 2 use cases:

with-universal-configuration - shows build time transpilation of environment variables. Should probably be renamed to with-universal-configuration-build-time

with-universal-configuration-runtime - should show the publicRuntimeConfig implementation. This means that environment variables can be set at runtime, but also means they have to be sent in the pre-rendered document so they have a very small cost