icu data files shipped in tzdata source package are generated and miss original form

[Benjamin Drung]

The tzdata source packages ships four files in debian/icu that are not built from source:

```
$ grep -i generated debian/icu/*
debian/icu/metaZones.txt:// Generated using tools/cldr/cldr-to-icu/build-icu-data.xml
debian/icu/timezoneTypes.txt:// Generated using tools/cldr/cldr-to-icu/build-icu-data.xml
debian/icu/windowsZones.txt:// Generated using tools/cldr/cldr-to-icu/build-icu-data.xml
debian/icu/zoneinfo64.txt:// >> !!! >> THIS IS A MACHINE-GENERATED FILE << !!! <<
```

They're not considered as the preferred form of modification. Please replace them with the original form and generate them with tools/cldr/cldr-to-icu/build-icu-data.xml during package build: https://github.com/unicode-org/icu/blob/main/tools/cldr/cldr-to-icu/build-icu-data.xml