Remove OLD_RAILS and NEW_RAILS constants

Also removes legacy ActiveJob test setup.

This should be safe since we do not support Rails versions older than 6
anyway.

Author: ellnix

spec/spec_helper.rb

@@ -36,9 +36,6 @@
 # Required for serializing objects similar to production environments
 GlobalID.app = 'meilisearch-test'
 
-OLD_RAILS = Gem.loaded_specs['rails'].version < Gem::Version.new('4.0')
-NEW_RAILS = Gem.loaded_specs['rails'].version >= Gem::Version.new('6.0')
-
 Dir["#{File.dirname(__FILE__)}/support/*.rb"].each { |file| require file }
 
 RSpec.configure do |c|

spec/support/active_record_schema.rb

@@ -17,12 +17,6 @@
 
 FileUtils.rm('data.sqlite3') if File.exist?('data.sqlite3')
 
-unless OLD_RAILS || NEW_RAILS
-  require 'active_job/test_helper'
-
-  ActiveJob::Base.queue_adapter = :test
-end
-
 def ar_schema
   @ar_schema ||= ActiveRecord::Schema.new
 end