disable developer experience from build

Step 1: What is changing in this MR?

This MR disables the Developer Experience from our build.

related !3770 (merged)

related https://gitlab.com/gitlab-com/marketing/digital-experience/buyer-experience/-/issues/3578

Production	Review app
https://about.gitlab.com/developer-experience/	should 404

Step 2: Ensure that your changes comply with the following, where applicable:

• I, the Assignee, have run Axe tools on any updated pages, and fixed the relevant accessibility issues.
• These changes work on both Safari, Chrome, and Firefox.
• These changes have been reviewed for Visual Quality Assurance and Functional Quality Assurance on Mobile, Desktop, and Tablet.
• These changes work with our Google Analytics and SEO tools.
• These changes have been documented as expected.

Build Variables:

• Use Contentful Preview API