Fix tests for integer-simple
A bunch of tests for integer-simple were now broken for a foolish reason:
unlike the integer-gmp case, there is no CorePrep optimization for turning
small integers directly into applications of S#.
Rather than port this optimization to integer-simple (which would involve
moving a bunch of integer-simple names into PrelNames), I switched
as many tests as possible to use Int.
The printing of Integer is already tested in print037.