Fix backport of project_creation_level migration

db/migrate/20190311132527_add_project_creation_level_to_namespaces.rb

-# frozen_string_literal: true
-
-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
-class AddProjectCreationLevelToNamespaces < ActiveRecord::Migration[5.0]
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  def up
-    unless column_exists?(:namespaces, :project_creation_level)
-      add_column :namespaces, :project_creation_level, :integer
-    end
-  end
-
-  def down
-    unless column_exists?(:namespaces, :project_creation_level)
-      remove_column :namespaces, :project_creation_level, :integer
-    end
-  end
-end