Drop unused Assembler::set_external_target_at() method.

src/arm/assembler-arm.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 785 matching lines @@
 
   // Given the address of the beginning of a call, return the address
   // in the instruction stream that the call will return from.
   INLINE(static Address return_address_from_call_start(Address pc));
 
   // This sets the branch destination (which is in the constant pool on ARM).
   // This is for calls and branches within generated code.
   inline static void deserialization_set_special_target_at(
       Address constant_pool_entry, Address target);
 
-  // This sets the branch destination (which is in the constant pool on ARM).
-  // This is for calls and branches to runtime code.
-  inline static void set_external_target_at(Address constant_pool_entry,
-                                            Address target);
-
   // Here we are patching the address in the constant pool, not the actual call
   // instruction.  The address in the constant pool is the same size as a
   // pointer.
   static const int kSpecialTargetSize = kPointerSize;
 
   // Size of an instruction.
   static const int kInstrSize = sizeof(Instr);
 
   // Distance between start of patched return sequence and the emitted address
   // to jump to.
@@ skipping 794 matching lines @@
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_ARM_H_