Don't use ZeroMap2d for metazones

[robertbastian]

This could be even smaller if we had one map for standard names, and one for daylight names. #5745

[Manishearth]

Do we know why this increases loc even though it decreases postcard? I imagine there's some reduplication happening in baked?

[robertbastian]

Baked data LOC is the same, and the actually in-binary size decreases, as can be seen in fingerprints.csv. JSON gets more verbose because of tuples.

[Manishearth]

oh, it's json size, okay. nice.

[sffc]

Lgtm