Use QueuesMetadata for duplicate jobs

What does this MR do and why?

This MR removes the MultiStore from Gitlab::Redis::QueuesMetadata and its related feature flags, replacing Gitlab::Redis::Queues in lib/gitlab/sidekiq_middleware/duplicate_jobs/duplicate_job.rb. The workload has been migrated on gstg and gprd, so removing the multistore will not lead to any changes.

Note that no migration is required since QueuesMetadata's config_fallback is Queues, i.e. it will be configured like Queues if config/redis.queues_metadata.yml or the queues_metadata key in config/redis.yml does not exist.

The original MR is !131736 (merged).

See issue: gitlab-com/gl-infra/scalability#925 (closed)

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.