[tex-live] new Unicode ICU library release

[Karl Berry]

    >> http://blog.unicode.org/2018/10/icu-63-released.html
    >> ...

    We need to find out whether we can, or should, use that new libicu for
    the upcoming TeX Live 2019 season.

I would expect so. As long as it doesn't require C++14, which I see no
sign of (yay).

Akira found that the latest poppler release does need C++14. I have
hopes that we will be able to drop poppler completely, since that
requirement is madness. --thanks, karl.