Remove the `syntaxError` utility function

According to the ES5 spec, calling `SyntaxError(arg)` is equivalent
to calling `new SyntaxError(arg)`, which removes the need for the
`syntaxError` utility function.

See:
 * http://es5.github.io/#x15.11.1
 * http://es5.github.io/#x15.11.2
Merge pull request #20 from d10/simplify-syntax-error

Remove the `syntaxError` utility function