c++: simplify

* data/skeletons/stack.hh (ssize): Remove, same as size.

TODO

@@ -146,17 +146,6 @@ Maybe we should exhibit the YYUNDEFTOK token.  It could also be assigned a
 semantic value so that yyerror could be used to report invalid lexemes.
 See also the item "$undefined" below.
 
-** C++
-Move to int everywhere instead of unsigned?  stack_size, etc.  The parser
-itself uses int (for yylen for instance), yet stack is based on size_t.
-
-Maybe locations should also move to ints.
-
-Paul Eggert already covered most of this.  But before publishing these
-changes, we need to ask our C++ users if they agree with that change, or if
-we need some migration path.  Could be a %define variable, or simply
-%require "3.5".
-
 * Bison 3.7
 ** Unit rules / Injection rules (Akim Demaille)
 Maybe we could expand unit rules (or "injections", see

data/skeletons/stack.hh

@@ -91,12 +91,6 @@ m4_define([b4_stack_define],
         return index_type (seq_.size ());
       }
 
-      std::ptrdiff_t
-      ssize () const YY_NOEXCEPT
-      {
-        return std::ptrdiff_t (size ());
-      }
-
       /// Iterator on top of the stack (going downwards).
       const_iterator
       begin () const YY_NOEXCEPT