Consider what to do with date+zone semantic skeletons #7117
Description
Related: #6690
The ICU TC recommended that CLDR consider removing date+zone from semantic skeletons. https://unicode-org.atlassian.net/browse/ICU-23233
We currently support this in 2.0, and I don't anticipate removing it from ICU4X in the short term. We should re-evaluate in 3.0.
CLDR ticket about removing this from semantic skeletons: https://unicode-org.atlassian.net/browse/CLDR-19066