fix warnings

Former-commit-id: 8e66fd302d4bb4a7a9d264b61047128671265e67

include/igl/doublearea.cpp

@@ -133,7 +133,7 @@ IGL_INLINE void igl::doublearea(
   #  define IGL_OMP_MIN_VALUE 1000
   #endif
   #pragma omp parallel for if (m>IGL_OMP_MIN_VALUE)
-  for(long int i = 0;i<m;i++)
+  for(size_t i = 0;i<m;i++)
   {
     //// Heron's formula for area
     //const typename Derivedl::Scalar arg =

include/igl/slice.cpp

@@ -185,8 +185,6 @@ IGL_INLINE void igl::slice_mask(
   const int dim,
   Eigen::PlainObjectBase<DerivedX> & Y)
 {
-  int xm = X.rows();
-  int xn = X.cols();
   switch(dim)
   {
     case 1: