`drain_filter` has opposite behavior of standard library version

[mbrubeck]

In methods like std::vec::Vec::drain_filter, the element is removed if the closure returns true. But in hashbrown::HashMap::drain_filter (#135) and hashbrown::HashSet::drain_filter (#179), the element is removed if the closure returns false. 😦

cc rust-lang/rust#59618

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Update: This is fixed in hashbrown 0.9.0. When upgrading from earlier versions, all callers must flip the meaning of the predicate passed to the drain_filter method. I have submitted pull requests to all the affected crates I could find.

[Amanieu]

That... seems unfortunate. I assume the proper behavior is the one in libstd and the behavior of hashbrown is incorrect.

This is going to have to be a (silent) breaking change, but that's fine since we can just do a major version bump.