[cleanup] Delete MacroAssembler::CopyBytes, it is dead code

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index c66a539208af1c9447e7712daf5ad1af7eac7aeb..442420e0df5baf04d26bb39f1866209767349402 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1528,18 +1528,6 @@ class MacroAssembler: public Assembler {
     return code_object_;
   }
 
-  // Copy length bytes from source to destination.
-  // Uses scratch register internally (if you have a low-eight register
-  // free, do use it, otherwise kScratchRegister will be used).
-  // The min_length is a minimum limit on the value that length will have.
-  // The algorithm has some special cases that might be omitted if the string
-  // is known to always be long.
-  void CopyBytes(Register destination,
-                 Register source,
-                 Register length,
-                 int min_length = 0,
-                 Register scratch = kScratchRegister);
-
   // Initialize fields with filler values.  Fields starting at |current_address|
   // not including |end_address| are overwritten with the value in |filler|.  At
   // the end the loop, |current_address| takes the value of |end_address|.