[NFC][regalloc] Remove unused API in AllocationOrder

[wmi]

LGTM.

Talk to Mircea offline. He confirmed that version 73f3d33dbbf2797d662eb12107b0ed5a8b91267f removed the use of the API in favor of the 'limit' alternative on next() but forgot to cleanup the dead API.

llvm/lib/CodeGen/AllocationOrder.h

unsigned next(unsigned Limit = 0) {
     while (Pos < int(Limit)) {
       unsigned Reg = Order[Pos++];
       if (!isHint(Reg))
         return Reg;
     }
     return 0;
   }
 
-  /// As next(), but allow duplicates to be returned, and stop before the
-  /// Limit'th register in the RegisterClassInfo allocation order.
-  ///
-  /// This can produce more than Limit registers if there are hints.
-  unsigned nextWithDups(unsigned Limit) {
-    if (Pos < 0)
-      return Hints.end()[Pos++];
-    if (HardHints)
-      return 0;
-    if (Pos < int(Limit))
-      return Order[Pos++];
-    return 0;
-  }
-
   /// Start over from the beginning.
   void rewind() { Pos = -int(Hints.size()); }
 
   /// Return true if the last register returned from next() was a preferred register.
   bool isHint() const { return Pos <= 0; }
 
   /// Return true if PhysReg is a preferred register.
   bool isHint(unsigned PhysReg) const { return is_contained(Hints, PhysReg); }
 };
 
 } // end namespace llvm
 
 #endif