You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: 20170123115500_remove_duplicate_indexes.rb
    path of file: ./repos/open-build-service/src/api/db/migrate
    
    the code of the file until where you have to start completion: class RemoveDuplicateIndexes < ActiveRecord::Mig
    
  def self.down
    # re-add duplicate indexes.
    # generated based the output of pt-duplicate-key-checker and the index definitions as of 7669128
    execute 'ALTER TABLE `attrib_namespace_modifiable_bies` ADD INDEX `index_attrib_namespace_modifiable_bies_on_attrib_namespace_id` (`attrib_namespace_id`);'
    execute 'ALTER TABLE `attrib_types` ADD INDEX `attrib_namespace_id` (`attrib_namespace_id`);'
    execute 'ALTER TABLE `binary_releases` ADD INDEX `index_binary_releases_on_binary_name` (`binary_name`);'
    execute 'ALTER TABLE `bs_request_actions` ADD INDEX `index_bs_request_actions_on_target_project_and_source_project` (`target_project`, `source_project`);'
    execute 'ALTER TABLE `cache_lines` ADD INDEX `index_cache_lines_on_project` (`project`);'
    execute 'ALTER TABLE `channels` ADD INDEX `package_id` (`package_id`);'
    execute 'ALTER TABLE `history_elements` ADD INDEX `index_history_elements_on_op_object_id` (`op_object_id`);'
    execute 'ALTER TABLE `package_issues` ADD INDEX `index_package_issues_on_package_id` (`package_id`);'
    execute 'ALTER TABLE `packages` ADD INDEX `index_packages_on_project_id` (`project_id`);'
    execute 'ALTER TABLE `reviews` ADD INDEX `index_reviews_on_state` (`state`);'
  end