[tz] Please remove tzdata2018f

[Florian Weimer]

* Stephen Colebourne:

> I believe the Java 8 parser requires the rearguard format, but it is
> not controlled by me anymore.
> https://bugs.openjdk.java.net/browse/JDK-8195595

Note that the more thorny issue is this one:

  <https://bugs.openjdk.java.net/browse/JDK-8212684>
  <https://bugs.openjdk.java.net/browse/JDK-8212970>

The current API follows POSIX and its requirements on hourly offsets,
and tzdata is no longer compatible with the POSIX specification of TZ
rules.

Thanks,
Florian