DownloadProvider: don't allow backups.

Change-Id: I5a07244d4bb7e11af4f5eb1a624fc20165248aab
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 56cdb9c..031b3d3 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -57,7 +57,8 @@
 
     <application android:process="android.process.media"
                  android:label="@string/app_label"
-                 android:icon="@mipmap/ic_launcher_download">
+                 android:icon="@mipmap/ic_launcher_download"
+                 android:allowBackup="false">
 
         <provider android:name=".DownloadProvider"
                   android:authorities="downloads" android:exported="true">