Remove the whats_new_featured_carousel ff

What does this MR do and why?

This change removes a feature flag that was controlling whether a "featured carousel" component appears in the "What's New" section of the application.

Previously, this carousel could be turned on or off using the feature flag, but now it will always be displayed to users.

References

Screenshots or screen recordings

No visual changes

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #554053 (closed)