[docs-infra] Fix use of process.env.DEPLOY_ENV

[oliviertassinari]

That check looked wrong to me. We have an env variable for this, which is replaced at build-time, so less bundle size, and that is more predictable.

(Initially added by Matt)

[mui-bot]

Netlify deploy preview

https://deploy-preview-43490--material-ui.netlify.app/

Bundle size report

No bundle size changes (Toolpad)
No bundle size changes

Generated by 🚫 dangerJS against af089ba

[alexfauquette]

Make me think that we are stoking and doing nothing with of all those comments

[oliviertassinari]

doing nothing with of all those comments

@alexfauquette They seem useful for new initiatives, when we are working our way toward product-market fit, we need to amplify any small feedback we can get. Also to spot obvious mistakes. After that, it's always more important to focus on 1. PR signal 2. issues signal, etc. These feedback become too easy to leave so doesn't tell enough about the intensity of the pain.

@samuelsycamore but maybe something to have in https://www.notion.so/mui-org/Head-of-Docs-49a20cef18dc4ccf8e6f50794964a144?pvs=4#cb890daeee8e4bdeb595c8f9a896f2a8?