Remove unreachable x64-specific function.

src/x64/assembler-x64-inl.h

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 159 matching lines @@
 
 
 void Operand::set_disp32(int32_t disp) {
   ASSERT(len_ == 1 || len_ == 2);
   int32_t* p = reinterpret_cast<int32_t*>(&buf_[len_]);
   *p = disp;
   len_ += sizeof(int32_t);
 }
 
 
-void Operand::set_dispr(intptr_t disp, RelocInfo::Mode rmode) {
-  // This cannot be used in 64-bit mode.  A 64-bit displacement
-  // cannot be encoded, so relocatable 64-bit values must be
-  // loaded as immediates.
-  UNIMPLEMENTED();
-}
-
-
 Operand::Operand(Register reg) {
   // reg
   set_modrm(3, reg);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_ASSEMBLER_X64_INL_H_