Remove migration dependency from stage_id migration

db/migrate/20170710083355_clean_stage_id_reference_migration.rb

-require Rails.root.join('db', 'post_migrate', '20170628080858_migrate_stage_id_reference_in_background')
-
 class CleanStageIdReferenceMigration < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
@@ -11,8 +9,7 @@ class CleanStageIdReferenceMigration < ActiveRecord::Migration
   # `MigrateStageIdReferenceInBackground` background migration cleanup.
   #
   def up
-    Gitlab::BackgroundMigration
-      .steal(MigrateStageIdReferenceInBackground::MIGRATION)
+    Gitlab::BackgroundMigration.steal('MigrateBuildStageIdReference')
   end
 
   def down

spec/migrations/clean_stage_id_reference_migration_spec.rb

 require 'spec_helper'
 require Rails.root.join('db', 'migrate', '20170710083355_clean_stage_id_reference_migration.rb')
+require Rails.root.join('db', 'post_migrate', '20170628080858_migrate_stage_id_reference_in_background')
 
 describe CleanStageIdReferenceMigration, :migration, :sidekiq, :redis do
   let(:migration) { MigrateStageIdReferenceInBackground::MIGRATION }
 
   context 'when there are pending background migrations' do
-    it 'processes enqueued jobs synchronously' do
+    it 'processes pending jobs synchronously' do
       Sidekiq::Testing.disable! do
         BackgroundMigrationWorker.perform_in(2.minutes, migration, [1])
         BackgroundMigrationWorker.perform_async(migration, [1])