Add proto flag "javanano_use_deprecated_package" to avoid build breakage

Change-Id: Iea8a7bc2bb385e066b3f972105224fee3eb7c894
diff --git a/protos/backup.proto b/protos/backup.proto
index f3ad0b6..e1af696 100644
--- a/protos/backup.proto
+++ b/protos/backup.proto
@@ -18,6 +18,7 @@
 
 package launcher_backup;
 
+option javanano_use_deprecated_package = true;
 option java_package = "com.android.launcher3.backup";
 option java_outer_classname = "BackupProtos";