fix native callback signature to match with C#

src/csharp/ext/grpc_csharp_ext.c

@@ -65,8 +65,6 @@ grpc_byte_buffer *string_to_byte_buffer(const char *buffer, size_t len) {
   return bb;
 }
 
-typedef void(GPR_CALLTYPE *callback_funcptr)(gpr_int32 success, void *batch_context);
-
 /*
  * Helper to maintain lifetime of batch op inputs and store batch op outputs.
  */
@@ -731,10 +729,12 @@ GPR_EXPORT void GPR_CALLTYPE grpcsharp_redirect_log(grpcsharp_log_func func) {
   gpr_set_log_function(grpcsharp_log_handler);
 }
 
+typedef void(GPR_CALLTYPE *test_callback_funcptr)(gpr_int32 success);
+
 /* For testing */
 GPR_EXPORT void GPR_CALLTYPE
-grpcsharp_test_callback(callback_funcptr callback) {
-  callback(1, NULL);
+grpcsharp_test_callback(test_callback_funcptr callback) {
+  callback(1);
 }
 
 /* For testing */