[C++] Remove useless include

src/algorithm/operational-frames.hpp

 //
-// Copyright (c) 2015 CNRS
+// Copyright (c) 2015-2016 CNRS
 //
 // This file is part of Pinocchio
 // Pinocchio is free software: you can redistribute it
@@ -18,9 +18,7 @@
 #ifndef __se3_operational_frames_hpp__
 #define __se3_operational_frames_hpp__
 
-#include "pinocchio/multibody/visitor.hpp"
 #include "pinocchio/multibody/model.hpp"
-#include "pinocchio/spatial/skew.hpp"
 
 #include "pinocchio/algorithm/kinematics.hpp"
 #include "pinocchio/algorithm/jacobian.hpp"