[MISched][NFC] Remove unused heuristic NextDefUse from enum

Heuristic was removed in 46533e6 due to being ineffective.

Author: c-rhodes

llvm/include/llvm/CodeGen/MachineScheduler.h

@@ -1080,7 +1080,7 @@ class GenericSchedulerBase : public MachineSchedStrategy {
   enum CandReason : uint8_t {
     NoCand, Only1, PhysReg, RegExcess, RegCritical, Stall, Cluster, Weak,
     RegMax, ResourceReduce, ResourceDemand, BotHeightReduce, BotPathReduce,
-    TopDepthReduce, TopPathReduce, NextDefUse, NodeOrder};
+    TopDepthReduce, TopPathReduce, NodeOrder};
 
 #ifndef NDEBUG
   static const char *getReasonStr(GenericSchedulerBase::CandReason Reason);

llvm/lib/CodeGen/MachineScheduler.cpp

@@ -3236,7 +3236,6 @@ const char *GenericSchedulerBase::getReasonStr(
   case TopPathReduce:  return "TOP-PATH  ";
   case BotHeightReduce:return "BOT-HEIGHT";
   case BotPathReduce:  return "BOT-PATH  ";
-  case NextDefUse:     return "DEF-USE   ";
   case NodeOrder:      return "ORDER     ";
   };
   llvm_unreachable("Unknown reason!");