Revert "Change ClassExt.originalDexFile field to an opaque Object"

Bug: 31455788

Fails on target.

This reverts commit d43e872bc6b6d24ce4b9554a27d5ab46c1f62c2e.

Change-Id: I7fefa1c075d654b8a0196b518bd33e4058f9a831
diff --git a/libart/src/main/java/dalvik/system/ClassExt.java b/libart/src/main/java/dalvik/system/ClassExt.java
index 3daa971..772bd2e 100644
--- a/libart/src/main/java/dalvik/system/ClassExt.java
+++ b/libart/src/main/java/dalvik/system/ClassExt.java
@@ -48,7 +48,7 @@
     private Object obsoleteMethods;
 
     /**
-     * If set, the bytes or DexCache of the original dex-file associated with the related class.
+     * If set, the bytes of the original dex-file associated with the related class.
      *
      * In this instance 'original' means either (1) the dex-file loaded for this class when it was
      * first loaded after all non-retransformation capable transformations had been performed but
@@ -59,7 +59,7 @@
      *
      * This field is a logical part of the 'Class' type.
      */
-    private Object originalDexFile;
+    private byte[] originalDexFile;
 
     /**
      * If class verify fails, we must return same error on subsequent tries. We may store either