Removed YYUSE [Bug #17582]

Although it was used just to suppress an "unsed argument" warning
in the same manner as other bison-provided functions, it has been
dropped since Bision 3.7.5.  And we always suppress that
warnings.

parse.y

@@ -13334,7 +13334,6 @@ count_char(const char *str, int c)
 RUBY_FUNC_EXPORTED size_t
 rb_yytnamerr(struct parser_params *p, char *yyres, const char *yystr)
 {
-    YYUSE(p);
     if (*yystr == '"') {
 	size_t yyn = 0, bquote = 0;
 	const char *yyp = yystr;