Remove the end-block handling code. It was unsafe, and making it safe would have...

Remove the end-block handling code.  It was unsafe, and making it safe would have resulted in falling back to the slow DSE case.  I need to think some more about the right way to handle this.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@39788 91177308-0d34-0410-b5e6-96231b3b80d8