Remove foreign key ci_minutes_additional_packs.namespace_id

In https://gitlab.com/gitlab-org/gitlab/-/merge_requests/77322 we
already added a ["loose foreign key"](
https://docs.gitlab.com/ee/development/database/loose_foreign_keys.html)
to replace this foreign key. Now that this has been running fine in
production we should be OK to remove the foreign key altogether.

This was added in a post-deployment migration as we want to ensure that
they have the correct code running with the loose foreign key in place
before we remove the foreign key to ensure that there isn't any lost
deletes.

Changelog: other

db/post_migrate/20220105020514_remove_ci_minutes_additional_packs_namespace_id_foreign_key_constraint.rb

+# frozen_string_literal: true
+
+class RemoveCiMinutesAdditionalPacksNamespaceIdForeignKeyConstraint < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  CONSTRAINT_NAME = 'fk_rails_e0e0c4e4b1'
+
+  def up
+    with_lock_retries do
+      remove_foreign_key_if_exists(:ci_minutes_additional_packs, :namespaces, name: CONSTRAINT_NAME)
+    end
+  end
+
+  def down
+    add_concurrent_foreign_key :ci_minutes_additional_packs, :namespaces, column: :namespace_id, on_delete: :cascade, name: CONSTRAINT_NAME
+  end
+end

db/schema_migrations/20220105020514

+301c2f09f48aa3e34c2f679628a9542b4babc589e3d20e9ccf84a9209f5841ee
\ No newline at end of file

db/structure.sql

@@ -31270,9 +31270,6 @@ ALTER TABLE ONLY analytics_cycle_analytics_group_stages
 ALTER TABLE ONLY bulk_import_export_uploads
     ADD CONSTRAINT fk_rails_dfbfb45eca FOREIGN KEY (export_id) REFERENCES bulk_import_exports(id) ON DELETE CASCADE;
 
-ALTER TABLE ONLY ci_minutes_additional_packs
-    ADD CONSTRAINT fk_rails_e0e0c4e4b1 FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE;
-
 ALTER TABLE ONLY label_priorities
     ADD CONSTRAINT fk_rails_e161058b0f FOREIGN KEY (label_id) REFERENCES labels(id) ON DELETE CASCADE;
 

ee/spec/models/ci/minutes/additional_pack_spec.rb

@@ -34,4 +34,10 @@ RSpec.describe Ci::Minutes::AdditionalPack, type: :model do
       it { is_expected.not_to validate_uniqueness_of(:purchase_xid) }
     end
   end
+
+  it_behaves_like 'cleanup by a loose foreign key' do
+    let!(:model) { create(:ci_minutes_additional_pack) }
+
+    let!(:parent) { model.namespace }
+  end
 end