Remove unnecessary util/serialize.h from content_mapblock.cpp

src/content_mapblock.cpp

@@ -26,7 +26,6 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 #include "tile.h"
 #include "gamedef.h"
 #include "util/numeric.h"
-#include "util/serialize.h"
 #include "util/directiontables.h"
 
 // Create a cuboid.