[turbofan] Remove unused PlainPrimitiveToNumber operator.

src/compiler/opcodes.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_OPCODES_H_
 #define V8_COMPILER_OPCODES_H_
 
 #include <iosfwd>
 
 // Opcodes for control operators.
@@ skipping 177 matching lines @@
   V(NumberShiftRight)              \
   V(NumberShiftRightLogical)       \
   V(NumberClz32)                   \
   V(NumberCeil)                    \
   V(NumberFloor)                   \
   V(NumberRound)                   \
   V(NumberTrunc)                   \
   V(NumberToInt32)                 \
   V(NumberToUint32)                \
   V(NumberIsHoleNaN)               \
-  V(PlainPrimitiveToNumber)        \
   V(StringToNumber)                \
   V(ChangeTaggedToInt32)           \
   V(ChangeTaggedToUint32)          \
   V(ChangeTaggedToFloat64)         \
   V(ChangeInt32ToTagged)           \
   V(ChangeUint32ToTagged)          \
   V(ChangeFloat64ToTagged)         \
   V(ChangeBoolToBit)               \
   V(ChangeBitToBool)               \
   V(Allocate)                      \
@@ skipping 220 matching lines @@
   }
 };
 
 std::ostream& operator<<(std::ostream&, IrOpcode::Value);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPCODES_H_