[turbofan] Remove unused typedef VirtualRegisterSet.

src/compiler/instruction.h

 // Copyright 2014 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_INSTRUCTION_H_
 #define V8_COMPILER_INSTRUCTION_H_
 
 #include <deque>
 #include <iosfwd>
 #include <map>
@@ skipping 1155 matching lines @@
     for (Instruction* instr : instructions_) {
       if (instr->IsCall()) return true;
     }
     return false;
   }
 
  private:
   friend std::ostream& operator<<(std::ostream& os,
                                   const PrintableInstructionSequence& code);
 
-  typedef std::set<int, std::less<int>, ZoneIntAllocator> VirtualRegisterSet;
   typedef ZoneMap<const Instruction*, SourcePosition> SourcePositionMap;
 
   Isolate* isolate_;
   Zone* const zone_;
   InstructionBlocks* const instruction_blocks_;
   SourcePositionMap source_positions_;
   IntVector block_starts_;
   ConstantMap constants_;
   Immediates immediates_;
   InstructionDeque instructions_;
@@ skipping 13 matching lines @@
 
 
 std::ostream& operator<<(std::ostream& os,
                          const PrintableInstructionSequence& code);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_INSTRUCTION_H_