Convenience functions for working with Dict
Keep elements which fails to satisfy the predicate.
This is functionaly equivalent to Dict.filter (not << predicate) dict.
removeWhen (\c v -> v == 1) Dict.fromList [("Mary", 1), ("Jack", 2), ("Jill", 1)] == Dict.fromList [("Jack", 2)]
Takes a key-fn and a list, creates a Dict which maps the key returned from key-fn, to a list of matching elements.