remove debug dump

source/core/arithmetic/Sum.cpp

@@ -138,8 +138,6 @@ XTensor Sum(const XTensor &a, const XTensor &b, DTYPE beta)
     /* computation */
     _Sum(&a, &b, &c, beta);
     
-    c.Dump(stderr, "c: ");
-    
     /* tensor connections */
     XLink::MakeLink(&a, &b, &c, MATH_SUM);
     XLink::AddParamToHead(&c, beta);