Bug in re-exporting `_∷=_` and `_─_` from `Data.List.Membership.Setoid`

[MatthewDaggitt]

Looking back through my huge backlog of standard library related emails, I found this comment by @gallais earlier this year

abbd3e7#r108952994

I assume this bug is still active.

[jamesmckinna]

A pity we didn't catch this during work on #2049 , but perhaps that offers a way out via remove etc.?