Move ensure_ivar_visibility! ruby method the the Java extension on JRuby

Author: pitr-ch

ext/com/concurrent_ruby/ext/SynchronizationLibrary.java

@@ -105,5 +105,10 @@ public IRubyObject nsBroadcast(ThreadContext context) {
             notifyAll();
             return this;
         }
+
+        @JRubyMethod(name = "ensure_ivar_visibility!", visibility = Visibility.PRIVATE)
+        public IRubyObject ensureIvarVisibilityBang(ThreadContext context) {
+            return context.nil;
+        }
     }
 }

lib/concurrent/synchronization.rb

@@ -1,7 +1,6 @@
 require 'concurrent/utility/engine'
 require 'concurrent/synchronization/abstract_object'
 require 'concurrent/native_extensions' # JavaObject
-require 'concurrent/synchronization/java_object' # JavaObject
 require 'concurrent/synchronization/mutex_object'
 require 'concurrent/synchronization/monitor_object'
 require 'concurrent/synchronization/rbx_object'