Remove the support for C++ namespace cleanliness; it was

Remove the support for C++ namespace cleanliness; it was
causing more problems than it was curing, since it didn't work
properly on some nonstandard C++ compilers.  This can wait
for a proper C++ parser.

* NEWS: Document this.
* doc/bison.texinfo (Bison Parser, Debugging): Remove special mention
of C++, as it's treated like C now.
* src/bison.simple (YYSTD): Remove.
(YYSIZE_T, YYFPRINTF, YYPARSE_PARAM_ARG, YYPARSE_PARAM_DECL):
Treat C++ just like Standard C instead of trying to support
namespace cleanliness.