Revert "MachineScheduler: better book-keeping for asserts."

This reverts commit r212088, which is causing a number of spec
failures.  Will provide reduced test cases shortly.
PR20057

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212109 91177308-0d34-0410-b5e6-96231b3b80d8