[Feature flag] Rollout of `use_redis_hll_instrumentation_classes`

What does this MR do and why?

Feature use_redis_hll_instrumentation_classes has been enabled on production since June 22 without any issue. This commits remove feature flag artifacts and release feature.

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How to set up and validate locally

Run follwing snippet on current branch:

redis_hll_payload = ServicePing::BuildPayload.new.execute["redis_hll_counters"]
migrated_categories = ::Gitlab::UsageDataCounters::HLLRedisCounter::CATEGORIES_COLLECTED_FROM_METRICS_DEFINITIONS

migrated_categories.map do |category|
  redis_hll_payload[category].size
end

=> [4, 6, 8, 6, 2, 6, 2, 2, 12, 2, 30, 6]

Checkout master branch, and toggle feature flag off

::Feature.disable(:use_redis_hll_instrumentation_classes)

Rerun

redis_hll_payload = ServicePing::BuildPayload.new.execute["redis_hll_counters"]
migrated_categories = ::Gitlab::UsageDataCounters::HLLRedisCounter::CATEGORIES_COLLECTED_FROM_METRICS_DEFINITIONS

migrated_categories.map do |category|
  redis_hll_payload[category].size
end

=> [4, 6, 8, 6, 2, 6, 2, 2, 12, 2, 30, 6]

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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.

Related to #365332 (closed)