[stubs] Remove dead string copying code

src/s390/code-stubs-s390.h

Index: src/s390/code-stubs-s390.h
diff --git a/src/s390/code-stubs-s390.h b/src/s390/code-stubs-s390.h
index 461e56902313cdf0b962cc9386471032ac60386d..f43dd3a0da2200f9bbaa564af6a9a97daedc6b50 100644
--- a/src/s390/code-stubs-s390.h
+++ b/src/s390/code-stubs-s390.h
@@ -14,15 +14,6 @@ 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 r0.
   static void GenerateCompareFlatOneByteStrings(MacroAssembler* masm,
                                                 Register left, Register right,