Remove ignore_column from ProjectSettings

project_settings.allow_editing_commit_messages was ignored in 14.2 and
the column was removed in 14.3. Following the dropping column process,
the `ignore_column` statement can be removed in 14.4

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/336783

app/models/project_setting.rb

 # frozen_string_literal: true
 
 class ProjectSetting < ApplicationRecord
-  include IgnorableColumns
-
-  ignore_column :allow_editing_commit_messages, remove_with: '14.4', remove_after: '2021-09-10'
-
   belongs_to :project, inverse_of: :project_setting
 
   enum squash_option: {