fix: Remove localized hreflang from Custom Pages

Step 1: What is changing in this MR?

• Remove the parameter that generates localized hreflangs for Custom pages, removing localized URLs of non-localized pages.

Production	Review app
https://about.gitlab.com/upgrade	https://3668-automated-issue-fix-596-broken-links.about.gitlab-review.app/upgrade

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

Related to #3668 (closed)