[MachineScheduler] Comments fixing.

The name/comment of the third argument to the ScheduleDAGMI constructor
is RemoveKillFlags and not IsPostRA. Only the comments are changed.

Review: A Trick
llvm-svn: 286350
diff --git a/llvm/lib/CodeGen/MachineScheduler.cpp b/llvm/lib/CodeGen/MachineScheduler.cpp
index 7946ca7..335578b 100644
--- a/llvm/lib/CodeGen/MachineScheduler.cpp
+++ b/llvm/lib/CodeGen/MachineScheduler.cpp
@@ -3267,7 +3267,8 @@
 
 /// Create a generic scheduler with no vreg liveness or DAG mutation passes.
 static ScheduleDAGInstrs *createGenericSchedPostRA(MachineSchedContext *C) {
-  return new ScheduleDAGMI(C, make_unique<PostGenericScheduler>(C), /*IsPostRA=*/true);
+  return new ScheduleDAGMI(C, make_unique<PostGenericScheduler>(C),
+                           /*RemoveKillFlags=*/true);
 }
 
 //===----------------------------------------------------------------------===//