Remove a dead method from lithium-* files.

src/mips/lithium-mips.h

 // Copyright 2012 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 2143 matching lines @@
   HGraph* graph() const { return graph_; }
 
   bool is_unused() const { return status_ == UNUSED; }
   bool is_building() const { return status_ == BUILDING; }
   bool is_done() const { return status_ == DONE; }
   bool is_aborted() const { return status_ == ABORTED; }
 
   void Abort(const char* format, ...);
 
   // Methods for getting operands for Use / Define / Temp.
-  LRegister* ToOperand(Register reg);
   LUnallocated* ToUnallocated(Register reg);
   LUnallocated* ToUnallocated(DoubleRegister reg);
 
   // Methods for setting up define-use relationships.
   MUST_USE_RESULT LOperand* Use(HValue* value, LUnallocated* operand);
   MUST_USE_RESULT LOperand* UseFixed(HValue* value, Register fixed_register);
   MUST_USE_RESULT LOperand* UseFixedDouble(HValue* value,
                                            DoubleRegister fixed_register);
 
   // A value that is guaranteed to be allocated to a register.
@@ skipping 97 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(LChunkBuilder);
 };
 
 #undef DECLARE_HYDROGEN_ACCESSOR
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_MIPS_LITHIUM_MIPS_H_