Revert "src: fix stuck debugger process"

This reverts commit ff877e93e1.

Reverted for breaking `node --debug-brk -e 0`.  It should immediately
quit but instead it hangs now.

PR-URL: https://github.com/nodejs/node/pull/3585
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node.cc

@@ -3747,6 +3747,7 @@ void Init(int* argc,
   uv_async_init(uv_default_loop(),
                 &dispatch_debug_messages_async,
                 DispatchDebugMessagesAsyncCallback);
+  uv_unref(reinterpret_cast<uv_handle_t*>(&dispatch_debug_messages_async));
 
 #if defined(NODE_V8_OPTIONS)
   // Should come before the call to V8::SetFlagsFromCommandLine()
@@ -4054,11 +4055,8 @@ static void StartNodeInstance(void* arg) {
     env->set_trace_sync_io(trace_sync_io);
 
     // Enable debugger
-    if (instance_data->use_debug_agent()) {
+    if (instance_data->use_debug_agent())
       EnableDebug(env);
-    } else {
-      uv_unref(reinterpret_cast<uv_handle_t*>(&dispatch_debug_messages_async));
-    }
 
     {
       SealHandleScope seal(isolate);