Revert "Don’t use TruffleRuby’s patch"

This reverts commit 2634128.

Author: eregon

lib/concurrent-ruby/concurrent/configuration.rb

@@ -1,14 +1,7 @@
 require 'thread'
 require 'concurrent/delay'
 require 'concurrent/errors'
-
-if Concurrent.on_truffleruby?
-  # Avoid TruffleRuby's patch
-  require File.expand_path('atomic/atomic_reference', __dir__)
-else
-  require 'concurrent/atomic/atomic_reference'
-end
-
+require 'concurrent/atomic/atomic_reference'
 require 'concurrent/concern/logging'
 require 'concurrent/concern/deprecation'
 require 'concurrent/executor/immediate_executor'