[stubs] Remove dead string copying code

src/x64/code-stubs-x64.h

 // Copyright 2011 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_X64_CODE_STUBS_X64_H_
 #define V8_X64_CODE_STUBS_X64_H_
 
 namespace v8 {
 namespace internal {
 
 
 void ArrayNativeCode(MacroAssembler* masm, Label* call_generic_code);
 
 
 class StringHelper : public AllStatic {
  public:
-  // Generate code for copying characters using the rep movs instruction.
-  // Copies rcx characters from rsi to rdi. Copying of overlapping regions is
-  // not supported.
-  static void GenerateCopyCharacters(MacroAssembler* masm,
-                                     Register dest,
-                                     Register src,
-                                     Register count,
-                                     String::Encoding encoding);
-
   // Compares two flat one-byte strings and returns result in rax.
   static void GenerateCompareFlatOneByteStrings(
       MacroAssembler* masm, Register left, Register right, Register scratch1,
       Register scratch2, Register scratch3, Register scratch4);
 
   // Compares two flat one-byte strings for equality and returns result in rax.
   static void GenerateFlatOneByteStringEquals(MacroAssembler* masm,
                                               Register left, Register right,
                                               Register scratch1,
                                               Register scratch2);
@@ skipping 323 matching lines @@
   RegisterAllocation regs_;
 
   DISALLOW_COPY_AND_ASSIGN(RecordWriteStub);
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_CODE_STUBS_X64_H_