c++: minor simplification

[Akim Demaille]

commit ba297917739b43e721bb790ffd24c22acfa52489
Author: Akim Demaille <address@hidden>
Date:   Sun Oct 21 19:09:53 2018 +0200

    c++: minor simplification
    
    * data/stack.hh: Prefer a default argument value to two constructors.

diff --git a/data/stack.hh b/data/stack.hh
index 1036eea1..e04ca023 100644
--- a/data/stack.hh
+++ b/data/stack.hh
@@ -36,12 +36,7 @@ m4_define([b4_stack_define],
     typedef typename S::const_reverse_iterator const_iterator;
     typedef typename S::size_type size_type;
 
-    stack ()
-    {
-      seq_.reserve (200);
-    }
-
-    stack (size_type n)
+    stack (size_type n = 200)
       : seq_ (n)
     {}