Fix missing cases of empty_string canonicalization

src/mips/macro-assembler-mips.h

Index: src/mips/macro-assembler-mips.h
diff --git a/src/mips/macro-assembler-mips.h b/src/mips/macro-assembler-mips.h
index bd8da85fb333800250fd014f04c55469dbf75096..9e4691327bdc18055f61b025c4222adb0859adcc 100644
--- a/src/mips/macro-assembler-mips.h
+++ b/src/mips/macro-assembler-mips.h
@@ -1743,12 +1743,6 @@ const Operand& rt = Operand(zero_reg), BranchDelaySlot bd = PROTECT
                       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,  // ne for new space, eq otherwise.