Removing Coins from a Pile

   (remove-coins-from-pile game-state n p) ; given a state, returns a new
                                           ; state with n fewer coins in pile p

To remove a number of coins n from pile p:

• Determine if p is 1 or 2

• Determine the size of pile p (use selector),

• Create a new game state with n coins removed from pile p (use constructor).