rm define

Former-commit-id: 71108f0329b22a139e9263a45ab3ee8fdfaf7a5a

include/igl/sum.h

@@ -8,7 +8,6 @@
 #ifndef IGL_SUM_H
 #define IGL_SUM_H
 #include "igl_inline.h"
-#define EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
 #include <Eigen/Sparse>
 
 namespace igl