Remove Runtime exit() function from Balls app.

This prevents a nasty teardown bug that was causing segfaults during atexit().
It is more than sufficient to call onStop() in this case to properly release
all resources.

Change-Id: If9ea892074382f9ea194da3d75771aae3b529053
diff --git a/samples/RenderScript/Balls/src/com/example/android/rs/balls/Balls.java b/samples/RenderScript/Balls/src/com/example/android/rs/balls/Balls.java
index 2a7436a..2c6558e 100644
--- a/samples/RenderScript/Balls/src/com/example/android/rs/balls/Balls.java
+++ b/samples/RenderScript/Balls/src/com/example/android/rs/balls/Balls.java
@@ -34,8 +34,6 @@
 import android.widget.Button;
 import android.widget.ListView;
 
-import java.lang.Runtime;
-
 import android.app.Activity;
 import android.content.Context;
 import android.os.Bundle;
@@ -100,7 +98,7 @@
     protected void onPause() {
         super.onPause();
         mView.pause();
-        Runtime.getRuntime().exit(0);
+        onStop();
     }
 
     @Override