Remove the loose_foreign_key_cleanup FF

This change removes the loose_foreign_key_cleanup feature flag.

Changelog: removed

app/workers/loose_foreign_keys/cleanup_worker.rb

@@ -12,8 +12,6 @@ module LooseForeignKeys
     idempotent!
 
     def perform
-      return if Feature.disabled?(:loose_foreign_key_cleanup, default_enabled: :yaml)
-
       in_lock(self.class.name.underscore, ttl: ModificationTracker::MAX_RUNTIME, retries: 0) do
         stats = {}
 

config/feature_flags/development/loose_foreign_key_cleanup.yml

----
-name: loose_foreign_key_cleanup
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/69165
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/343545
-milestone: '14.4'
-type: development
-group: group::sharding
-default_enabled: true

spec/workers/loose_foreign_keys/cleanup_worker_spec.rb

@@ -141,16 +141,6 @@ RSpec.describe LooseForeignKeys::CleanupWorker do
     end
   end
 
-  context 'when the loose_foreign_key_cleanup feature flag is off' do
-    before do
-      stub_feature_flags(loose_foreign_key_cleanup: false)
-    end
-
-    it 'does nothing' do
-      expect { described_class.new.perform }.not_to change { LooseForeignKeys::DeletedRecord.status_processed.count }
-    end
-  end
-
   describe 'multi-database support' do
     where(:current_minute, :configured_base_models, :expected_connection) do
       2 | { main: ApplicationRecord, ci: Ci::ApplicationRecord } | ApplicationRecord.connection