parse.y: removed useless check

* parse.y (singleton): literal nodes are always value expressions,
  no check is necessary.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59601 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

parse.y

@@ -4673,6 +4673,7 @@ singleton	: var_ref
 			      case NODE_ARRAY:
 			      case NODE_ZARRAY:
 				yyerror("can't define singleton method for literals");
+				break;
 			      default:
 				value_expr($3);
 				break;