[stubs] Remove dead string copying code

src/mips64/code-stubs-mips64.h

Index: src/mips64/code-stubs-mips64.h
diff --git a/src/mips64/code-stubs-mips64.h b/src/mips64/code-stubs-mips64.h
index fdaf4c80df0c7ccabb7f2ae30fbcd5fee6e0330c..b619bf9c147a95473f4fcab71fe1c2cb59ddf392 100644
--- a/src/mips64/code-stubs-mips64.h
+++ b/src/mips64/code-stubs-mips64.h
@@ -16,17 +16,6 @@ void ArrayNativeCode(MacroAssembler* masm, Label* call_generic_code);
 
 class StringHelper : public AllStatic {
  public:
-  // Generate code for copying a large number of characters. This function
-  // is allowed to spend extra time setting up conditions to make copying
-  // faster. Copying of overlapping regions is not supported.
-  // Dest register ends at the position after the last character written.
-  static void GenerateCopyCharacters(MacroAssembler* masm,
-                                     Register dest,
-                                     Register src,
-                                     Register count,
-                                     Register scratch,
-                                     String::Encoding encoding);
-
   // Compares two flat one-byte strings and returns result in v0.
   static void GenerateCompareFlatOneByteStrings(
       MacroAssembler* masm, Register left, Register right, Register scratch1,