Ocean zones could partake in deduplication

[robertbastian]

For example Europe/Moscow and Etc/GMT-3 agree on all future timestamps, but both zones are included in timezones-with-oceans-now. This requires unnecessary boundaries, i.e. big parts of the east coast of Africa, Madagascar, the coast of the Arabian peninsula, etc are all borders between Europe/Moscow and Etc/GMT-3 that aren't necessary.

Deduplicating the Etc/ zones would remove the outlines of many coast lines (those in the "correct" time zone year-round), reducing data size. It would also align timezones-with-oceans-now with zonetab.now, which doesn't include any Etc/ zones (as there's a populated zone for each offset).

[robertbastian]

This removes all Etc/ time zones except for Etc/GMT+12, as that time zone is actually not used anywhere outside nautical time.