Drop NaCl support for posting stdout/stderr to JS.

ppapi/native_client/src/trusted/plugin/service_runtime.cc

Index: ppapi/native_client/src/trusted/plugin/service_runtime.cc
diff --git a/ppapi/native_client/src/trusted/plugin/service_runtime.cc b/ppapi/native_client/src/trusted/plugin/service_runtime.cc
index ffce56320dedd85df0dc9ae4d7f82fa6291d2142..b162f62f854a1f2d5cda0683f4b5086a58794a0f 100644
--- a/ppapi/native_client/src/trusted/plugin/service_runtime.cc
+++ b/ppapi/native_client/src/trusted/plugin/service_runtime.cc
@@ -84,9 +84,8 @@ void PluginReverseInterface::ShutDown() {
 }
 
 void PluginReverseInterface::DoPostMessage(nacl::string message) {
-  std::string full_message = std::string("DEBUG_POSTMESSAGE:") + message;
-  GetNaClInterface()->PostMessageToJavaScript(pp_instance_,
-                                              full_message.c_str());
+  // This feature is no longer used.
+  // TODO(teravest): Remove this once this is gone from nacl::ReverseInterface.
 }
 
 void PluginReverseInterface::StartupInitializationComplete() {