Remove unused "InitFromImageCallbackState"

Change-Id: Ie434b2e74971df6c3b22f4d492f7b71155e3da3e
diff --git a/src/class_linker.h b/src/class_linker.h
index 8e474df..8ad8d2d 100644
--- a/src/class_linker.h
+++ b/src/class_linker.h
@@ -300,7 +300,6 @@
   void InitFromImage();
   OatFile* OpenOat(const ImageSpace* space);
   static void InitFromImageCallback(Object* obj, void* arg);
-  struct InitFromImageCallbackState;
 
   void FinishInit();