Remove feature flags used for utilizing load balancing capabilities in UserRefreshOverUserRangeWorker [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

For #327092 (closed)

The rollout of these 2 flags on gitlab.com are now complete, and both these flags are enabled 100% of the time.

The metrics and performance after enabling are as expected, so it is safe to remove these 2 flags now.

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
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Availability and Testing

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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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