Cleanup index terraform module archive FF

What does this MR do and why?

In Parse and create terraform module metadata (!148569 - merged), we introduced a background worker to parse the uploaded terraform modules and extract their metadata. The worker invocation is behind a feature flag. The flag was rolled out on gitlab.com and things deemed stable for a while now. In this MR, we clean up the feature flag from the codebase and release the feature.

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Related to #438058 (closed)