[core] Render from the main thread

Do not create a thread for the MapContext anymore.

platform/node/src/node_mapbox_gl_native.cpp

@@ -5,25 +5,18 @@
 #include <nan.h>
 #pragma GCC diagnostic pop
 
-#include "node_mapbox_gl_native.hpp"
+#include <mbgl/util/run_loop.hpp>
+
 #include "node_map.hpp"
 #include "node_log.hpp"
 #include "node_request.hpp"
 
-namespace node_mbgl {
-
-mbgl::util::RunLoop& NodeRunLoop() {
-    static mbgl::util::RunLoop nodeRunLoop;
-    return nodeRunLoop;
-}
-
-}
-
 void RegisterModule(v8::Local<v8::Object> target, v8::Local<v8::Object> module) {
     // This has the effect of:
     //   a) Ensuring that the static local variable is initialized before any thread contention.
     //   b) unreffing an async handle, which otherwise would keep the default loop running.
-    node_mbgl::NodeRunLoop().stop();
+    static mbgl::util::RunLoop nodeRunLoop;
+    nodeRunLoop.stop();
 
     node_mbgl::NodeMap::Init(target);
     node_mbgl::NodeRequest::Init(target);