[mk-sbuild] schroot made by mk-sbuild have broken TZ info

[Simon Chopin]

mk-sbuild copies /etc/timezone and /etc/localtime to the schroots it creates, but tzdata is not part of the default package set, resulting in /etc/localtime being a broken symlink and the actual time zone as reported by `date(1)` is UTC no matter what /etc/timezone reports.

I think this should be removed from mk-sbuild since it doesn't work as intended, and it can have side-effects breaking builds in non-obvious ways, since some package have embedded timezone data (e.g. icu) that can mismatch with the system. icu's test suite is broken by this, with failures in the test intltest::tztest::TestGenericAPI.

[Simon Chopin (schopin)]

It could be argued that src:icu should build-depend on tzdata, but I still think mk-sbuild is doing the wrong thing here.