revert parallel search on balance group examples

examples/dotnet/BalanceGroupSat.cs

@@ -144,7 +144,6 @@ public class BalanceGroupSat
         model.Minimize(e);
 
         var solver = new CpSolver();
-        solver.StringParameters = "num_search_workers:8";
 
         var solutionPrinter = new SolutionPrinter(values, colors, allGroups, allItems, itemInGroup);
 

examples/python/balance_group_sat.py

@@ -158,8 +158,9 @@ def main():
     # Minimize epsilon
     model.Minimize(e)
 
+    model.ExportToFile('balance_group_sat.pbtxt')
+
     solver = cp_model.CpSolver()
-    solver.parameters.num_search_workers = 8
     solution_printer = SolutionPrinter(values, colors, all_groups, all_items,
                                        item_in_group)
     status = solver.SolveWithSolutionCallback(model, solution_printer)