We dropped serialization of unions from (most) c++ sketches with the move to 2.0, but we have a JIRA from a while ago that notes we forgot to remove deserialize() form hll_union.
It's easy enough to remove the methods. But it's actually possible to pass in a regular HLL sketch to deserialize(), since the union just serialized its internal gadget (in this case I believe it's _always_ a proper HLL sketch; that's not true for other union gadgets). So would we need to move to 3.0 just for removing the deserialize() methods? I think strict semantic versioning would say yes? We haven't had it marked as officially deprecated, although the JIRA suggests it was already kinda of obvious. I removed the code locally and didn't even need to change unit tests or the python wrapper. So I can do the PR, but I'm not sure that we want to jump to 3.0 just for this change. Thoughts? jon
