Remove feature flag for npm packages existance check refactor

What does this MR do and why?

The feature flag was globally enabled on gitlab.com on 2025-08-06 #558119 (comment 2672288713). So far, no errors were observed logs (internal). Thus we could go ahead and remove feature flag.

This MR removes feature flag for npm packages existance check refactor.

References

Foundation: Prepare application code to read fr... (#548761 - closed)

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No.

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Related to #558119 (closed)