Consider dropping TZDB updates for 1.x

[jskeet]

Using nuget.org for metrics, 1.x is hardly used nowadays. We probably don't need to keep it up to date with TZDB.

It would be reasonable to keep it supported in terms of any significant bugs found in it, but that's all I suggest we do.
(I'm about to release 2018h in 1.4.x, but this may be the last one. And it's possible that I may not even do that if it proves tricky on my new machine...)

[jskeet]

It looks like this is actually relatively hard to achieve - even finding the .NET 3.5 SDK (let alone the client profile and PCL profiles) is tricky.
It may be time to retire the 1.x line.

For the moment I'm just releasing 2.4.3 for 2018h. We can create a 1.4.x with 2018h in if discussion here suggests it's worthwhile.

[jskeet]

Version 1.4.7, released on 2018-10-28, now has 1968 downloads, according to nuget.org.
Version 2.4.2 was released on the same date but superseded on 2018-12-30 - and had 262,908 downloads.

That makes it pretty obvious that it's not worth going to extraordinary lengths to support 1.x.

I'm adjusting the documentation accordingly, and closing this issue.