Remove unused field from AssetManager.

This field was introduced in commit 4bdd33b81a17 but wasn't
used there (or since).

Change-Id: I0615e98b8990d42da6b85f8094ab19eb0465fd9e

core/java/android/content/res/AssetManager.java

@@ -70,7 +70,6 @@ public final class AssetManager {
     
     // For communication with native code.
     private int mObject;
-    private int mNObject;  // used by the NDK
 
     private StringBlock mStringBlocks[] = null;