Silence incorrect assigned but unused variable warnings in ripper

To only emit the warnings in correct cases would require tracking
local variable usage in ripper, which ripper currently does not do.

Fixes [Bug #15188]

parse.y

@@ -11723,11 +11723,13 @@ warn_unused_var(struct parser_params *p, struct local_vars *local)
     if (cnt != local->vars->pos) {
 	rb_parser_fatal(p, "local->used->pos != local->vars->pos");
     }
+#ifndef RIPPER
     for (i = 0; i < cnt; ++i) {
 	if (!v[i] || (u[i] & LVAR_USED)) continue;
 	if (is_private_local_id(v[i])) continue;
 	rb_warn1L((int)u[i], "assigned but unused variable - %"PRIsWARN, rb_id2str(v[i]));
     }
+#endif
 }
 
 static void