style: rename semanticVal as value

* data/skeletons/README-D.txt: Remove, now useless and obsolete.
* data/skeletons/glr2.cc, examples/d/calc/calc.y,
* tests/calc.at, tests/d.at, tests/scanner.at (semanticVal): Replace
with...
(value): this.

tests/d.at

@@ -78,8 +78,6 @@ class CalcLexer(R) : Lexer
 
   void yyerror(string s) {}
 
-  Value semanticVal_;
-
   Symbol yylex()
   {
     $2