convert: drop a duplicate implementation of `dateutil.makedate()` I noticed this because the signature generated by pytype recently changed to be less specific. When the method was introduced back in 337d728e644f, `util.makedate()` didn't take an optional timestamp arg. But now it does, and the methods are the same (except the `dateutil` version validates that the timestamp isn't a negative value). I left the old method in place in case anyone has custom convert code that monkey patches it.