cldr: use CLDR 31.0.1 (and fix test changes); see below!

cldr: use CLDR 31.0.1 (and fix test changes); see below!

CLDR 31.0 separated the GMT and UTC time zones, so formatting of that
time zone has changed.  Most notably, "UTC" replaces "+0000" when formatting
the timezone.  This could break code that expects +0000.

A subset (the parts supported by Babel) of the migration guide from
http://cldr.unicode.org/index/downloads/cldr-31:

* The locales in the language-territory population tables have been changed to
  be the canonical format, dropping the script where it is the default.
  So "ku_Latn" changes to "ku".
* Plural rules: The Portuguese plural rules have changed so that all
  (and only) integers and decimal fractions < 2 are singular.
* Timezones: The GMT timezone has been split from the UTC timezone.
* Timezones: New timezone bcp47 codes have been added.
* Languages "hr" and "sr" are no longer a short distance apart, for political reasons.
* The primary names for CZ changed from "Czech Republic" to
  "Czechia", with the longer name now the alternate.