Remove guideline comments from migration

db/migrate/20210504085144_add_index_on_web_hook_project_id_recent_failures.rb

 # frozen_string_literal: true
 
-# See https://docs.gitlab.com/ee/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 class AddIndexOnWebHookProjectIdRecentFailures < ActiveRecord::Migration[6.0]
   include Gitlab::Database::MigrationHelpers