Eliminate String::Extend weak reference

Rarely used, mostly at boot, and probably just as quick to look up
the constant as go through the weak reference.

Author: headius

java/src/json/ext/GeneratorMethods.java

@@ -171,9 +171,9 @@ private static RubyHash toJsonRawObject(ThreadContext context,
         }
 
         @JRubyMethod(module=true)
-        public static IRubyObject included(ThreadContext context, IRubyObject vSelf, IRubyObject module) {
+        public static IRubyObject included(ThreadContext context, IRubyObject extendModule, IRubyObject module) {
             RuntimeInfo info = RuntimeInfo.forRuntime(context.runtime);
-            return module.callMethod(context, "extend", info.stringExtendModule.get());
+            return module.callMethod(context, "extend", ((RubyModule) extendModule).getConstant("Extend"));
         }
     }
 

java/src/json/ext/RuntimeInfo.java

@@ -28,8 +28,6 @@ final class RuntimeInfo {
     // the Ruby runtime object, which would cause memory leaks in the runtimes map above.
     /** JSON */
     WeakReference<RubyModule> jsonModule;
-    /** JSON::Ext::Generator::GeneratorMethods::String::Extend */
-    WeakReference<RubyModule> stringExtendModule;
     /** JSON::Ext::Generator::State */
     WeakReference<RubyClass> generatorStateClass;
     /** JSON::SAFE_STATE_PROTOTYPE */