Fix the tzdata update tools.

Fix the tzdata update tools.

The recent libcore ZoneInfo changes mean that we can no longer
compile libcore's ZoneInfo against the RI. Luckily, the field in
our data file that we needed ZoneInfo for isn't actually used.
This change removes our dependence on libcore.

I've left the field in to avoid a file format change. We can remove
the field if/when we next have a real need to bump the file format.

(cherry-pick of 90cb5ffb85a9bc2e725824b3ca8db932d02c45db.)

Bug: 16168653
Change-Id: Iedad2252c2b49f4d8bb2c7d9078b39b622444ca7