Redundant `Hashable` constraints on `intersection*` and `union*`

[sjakobi]

These functions don't compute any hashes, so we could consider removing the redundant constraints.

[treeowl]

Yank them, as far as I'm concerned. Did the previous intersection implementation need that?

[sjakobi]

Did the previous intersection implementation need that?

Yeah. It was based on unsafeInsert, so it was re-computing hashes.