A64: Synchronize with r18084.

src/a64/assembler-a64.h

Index: src/a64/assembler-a64.h
diff --git a/src/a64/assembler-a64.h b/src/a64/assembler-a64.h
index a27e1049c2452dbcf8a8948ea6d3161c334029fe..65bde2aa5791869ca6ae7b6247a437f94b9ba623 100644
--- a/src/a64/assembler-a64.h
+++ b/src/a64/assembler-a64.h
@@ -745,11 +745,6 @@ class Assembler : public AssemblerBase {
   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);
-
   // All addresses in the constant pool are the same size as pointers.
   static const int kSpecialTargetSize = kPointerSize;