Ord on Time may be misleading; consider removing in 3.0

[sffc]

Time values are cyclic, and in real life they are usually associated with a time zone. For both of these reasons, an Ord impl on Times might be misleading.

If we removed the impl, we should add a total_cmp function similar to the one we have on Locale and LanguageIdentifier so that clients can still access the behavior and write their own Ord wrapper if needed.

See #7035 (comment)

CC @michalmoc

[robertbastian]

The semantics of Time are time-of-day, which is perfectly comparable. Months are also cyclic, yet MonthCode is Ord. You shouldn't compare MonthCodes from different calendars or years, the same way you shouldn't compare Times obtained from different time zones or days. But it's convenient to have an Ord implementation.