Drop unused Assembler::set_external_target_at() method.

src/ia32/assembler-ia32.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 620 matching lines @@
   // of that call in the instruction stream.
   inline static Address target_address_from_return_address(Address pc);
 
   // This sets the branch destination (which is in the instruction on x86).
   // This is for calls and branches within generated code.
   inline static void deserialization_set_special_target_at(
       Address instruction_payload, Address target) {
     set_target_address_at(instruction_payload, target);
   }
 
-  // This sets the branch destination (which is in the instruction on x86).
-  // This is for calls and branches to runtime code.
-  inline static void set_external_target_at(Address instruction_payload,
-                                            Address target) {
-    set_target_address_at(instruction_payload, target);
-  }
-
   static const int kSpecialTargetSize = kPointerSize;
 
   // Distance between the address of the code target in the call instruction
   // and the return address
   static const int kCallTargetAddressOffset = kPointerSize;
   // Distance between start of patched return sequence and the emitted address
   // to jump to.
   static const int kPatchReturnSequenceAddressOffset = 1;  // JMP imm32.
 
   // Distance between start of patched debug break slot and the emitted address
@@ skipping 616 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_ASSEMBLER_IA32_H_