Remove a unused variable

In commit 1c35a3f6 a useless
computation that used the variable was removed.

storage/innobase/fsp/fsp0fsp.cc

 /*****************************************************************************
 
 Copyright (c) 1995, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2020, MariaDB Corporation.
+Copyright (c) 2017, 2021, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -2799,7 +2799,7 @@ fsp_reserve_free_extents(
 		return(true);
 	}
 try_to_extend:
-	if (ulint n = fsp_try_extend_data_file(space, space_header, mtr)) {
+	if (fsp_try_extend_data_file(space, space_header, mtr)) {
 		goto try_again;
 	}