Revert "Moving more MPI calls to the wrapper"

This reverts commit 0f91767b6c.

tests/TestMicroCTReader.cpp

@@ -62,6 +62,7 @@ int main(int argc, char **argv)
     int N_errors = ut.NumFailGlobal();
 
     // Close MPI
+    MPI_Barrier(MPI_COMM_WORLD);
     MPI_Finalize();
     return N_errors;
 }