Remove the CycleBound computation code from the ScheduleDAGRRList

Remove the CycleBound computation code from the ScheduleDAGRRList
schedulers. This doesn't have much immediate impact because
targets that use these schedulers by default don't yet provide
pipeline information.

This code also didn't have the benefit of register pressure
information. Also, removing it will avoid problems with list-burr
suddenly starting to do latency-oriented scheduling on x86 when we
start providing pipeline data, which would increase spilling.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@59775 91177308-0d34-0410-b5e6-96231b3b80d8