Merge 2D mpi versions. Cleanup.

BasicSolver/3D-mpi/src/comm.c

@@ -4,9 +4,6 @@
  * Use of this source code is governed by a MIT style
  * license that can be found in the LICENSE file.
  */
-#if defined(_MPI)
-#include <mpi.h>
-#endif
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -180,7 +177,7 @@ static int sum(int* sizes, int position)
 
     return sum;
 }
-#endif
+#endif // defined _MPI
 
 // exported subroutines
 void commReduction(double* v, int op)