Remove irrelevant comments

db/migrate/20160716115710_add_when_and_yaml_variables_to_ci_builds.rb

-# See http://doc.gitlab.com/ce/development/migration_style_guide.html
-# for more information on how to write migrations for GitLab.
-
 class AddWhenAndYamlVariablesToCiBuilds < ActiveRecord::Migration
   include Gitlab::Database::MigrationHelpers
 
-  # When using the methods "add_concurrent_index" or "add_column_with_default"
-  # you must disable the use of transactions as these methods can not run in an
-  # existing transaction. When using "add_concurrent_index" make sure that this
-  # method is the _only_ method called in the migration, any other changes
-  # should go in a separate migration. This ensures that upon failure _only_ the
-  # index creation fails and can be retried or reverted easily.
-  #
-  # To disable transactions uncomment the following line and remove these
-  # comments:
-  # disable_ddl_transaction!
-
   def change
     add_column :ci_builds, :when, :string
     add_column :ci_builds, :yaml_variables, :text