remove dead code

src/KSPACE/ewald_disp.cpp

@@ -1129,8 +1129,6 @@ void EwaldDisp::compute_energy_peratom()
 
 /* ---------------------------------------------------------------------- */
 
-#define swap(a, b) { double t = a; a= b; b = t; }
-
 void EwaldDisp::compute_virial()
 {
   memset(virial, 0, 6*sizeof(double));