comment out (most likely) unused code.

hs/DataStructures.hs

@@ -122,9 +122,10 @@ data BankersQueue a = BankersQueue {
enqueue x (BankersQueue fs f rs r) = check $ BankersQueue fs f (rs + 1) (cons x r)
dequeue (BankersQueue fs Nil         rs Nil) = Nothing
dequeue (BankersQueue fs Nil         rs r) = Just (x, check $ BankersQueue fs Nil (rs - 1) r')
    where (Just x) = last r
          r' = butLast r
-- not needed because of `check` invariant?
--dequeue (BankersQueue fs Nil         rs r) = Just (x, check $ BankersQueue fs Nil (rs - 1) r')
--    where (Just x) = last r
--          r' = butLast r
dequeue (BankersQueue fs (Cons x fr) rs r) =
    Just (x, check $ BankersQueue (fs - 1) fr rs r)