After 9c260fde (time: New package that mirrors Go's time) we have
golang.time.now and golang.time.sleep and it makes it a more
self-dependent system if timing facility is used through golang.time
instead of outside std time module.

For now this is only a "cleanness" change, but will become important once
we start adding pyx-level nogil API to pygolang - there it will be
important to use golang.time.* for correctness.