Remove unused 'using namespace std' lines.

src/http.cc

@@ -13,7 +13,6 @@
 
 using namespace v8;
 using namespace node;
-using namespace std;
 
 Persistent<FunctionTemplate> HTTPConnection::client_constructor_template;
 Persistent<FunctionTemplate> HTTPConnection::server_constructor_template;

src/node.cc

@@ -21,7 +21,6 @@
 
 using namespace v8;
 using namespace node;
-using namespace std;
 
 static void
 buf_free (evnet_buf *b)