Fix missing cases of empty_string canonicalization

src/ppc/macro-assembler-ppc.h

Index: src/ppc/macro-assembler-ppc.h
diff --git a/src/ppc/macro-assembler-ppc.h b/src/ppc/macro-assembler-ppc.h
index 8351ca44ff18866092f831e8eec1d82d841fae83..87e85a6b265493472279c87535508d1f6bcd9d86 100644
--- a/src/ppc/macro-assembler-ppc.h
+++ b/src/ppc/macro-assembler-ppc.h
@@ -1504,10 +1504,6 @@ class MacroAssembler : public Assembler {
                       bool* definitely_mismatches, InvokeFlag flag,
                       const CallWrapper& call_wrapper);
 
-  void InitializeNewString(Register string, Register length,
-                           Heap::RootListIndex map_index, Register scratch1,
-                           Register scratch2);
-
   // Helper for implementing JumpIfNotInNewSpace and JumpIfInNewSpace.
   void InNewSpace(Register object, Register scratch,
                   Condition cond,  // eq for new space, ne otherwise.