Remove ci_register_job_service_one_by_one feature flag

This commit removes ci_register_job_service_one_by_one feature flag
to Ci::RegisterJobService which makes builds queuing more efficient.

Changelog: changed

app/services/ci/register_job_service.rb

@@ -125,20 +125,12 @@ module Ci
         builds = builds.queued_before(params[:job_age].seconds.ago)
       end
 
-      if Feature.enabled?(:ci_register_job_service_one_by_one, runner, default_enabled: true)
-        build_ids = retrieve_queue(-> { builds.pluck(:id) })
+      build_ids = retrieve_queue(-> { builds.pluck(:id) })
 
-        @metrics.observe_queue_size(-> { build_ids.size }, @runner.runner_type)
+      @metrics.observe_queue_size(-> { build_ids.size }, @runner.runner_type)
 
-        build_ids.each do |build_id|
-          yield Ci::Build.find(build_id)
-        end
-      else
-        builds_array = retrieve_queue(-> { builds.to_a })
-
-        @metrics.observe_queue_size(-> { builds_array.size }, @runner.runner_type)
-
-        builds_array.each(&blk)
+      build_ids.each do |build_id|
+        yield Ci::Build.find(build_id)
       end
     end
     # rubocop: enable CodeReuse/ActiveRecord

config/feature_flags/development/ci_register_job_service_one_by_one.yml

----
-name: ci_register_job_service_one_by_one
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55194
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/323177
-milestone: '13.10'
-type: development
-group: group::memory
-default_enabled: true

spec/services/ci/register_job_service_spec.rb

@@ -711,11 +711,7 @@ module Ci
         end
       end
 
-      context 'when ci_register_job_service_one_by_one is enabled' do
-        before do
-          stub_feature_flags(ci_register_job_service_one_by_one: true)
-        end
-
+      context 'when a long queue is created' do
         it 'picks builds one-by-one' do
           expect(Ci::Build).to receive(:find).with(pending_job.id).and_call_original
 
@@ -725,14 +721,6 @@ module Ci
         include_examples 'handles runner assignment'
       end
 
-      context 'when ci_register_job_service_one_by_one is disabled' do
-        before do
-          stub_feature_flags(ci_register_job_service_one_by_one: false)
-        end
-
-        include_examples 'handles runner assignment'
-      end
-
       context 'when joining with pending builds table' do
         before do
           stub_feature_flags(ci_pending_builds_queue_join: true)