[SimplifyCFG] NFC, one more fixed test from previous push.

The old test was checking for a stupid subtract one that is a transform that
makes the code woorse.

The constant-islands-jump-table.ll test wants the code a specific way,
that makes sense, so I will submit code to fix that one.

Sorry that I really didn't know how to run the test suite before this.

llvm-svn: 361733