tz_localize_to_utc scalar version?
This can be shunted into the tslibs todo list after it has been seen.

`tslibs.conversion.tz_localize_to_utc` has a comment `# Vectorized version of DstTzInfo.localize`.  Two of the places where `tz_localize_to_utc` are called are for a singleton `np.array([self.value], dtype='i8')`.   If there is a scalar version available, we can avoid array creation and iteration overhead.