rm unnecessary include

Former-commit-id: 0050d862c56908ca2403efc37e6f43ec472c358a

include/igl/barycentric_coordinates.cpp

@@ -7,7 +7,6 @@
 // obtain one at http://mozilla.org/MPL/2.0/.
 #include "barycentric_coordinates.h"
 #include "volume.h"
-#include "doublearea.h"
 
 template <
   typename DerivedP,