Do not use a user tag on apps, as it is ignored.

The build system does not honor user tags on apps,
and setting it is misleading.

This removes the confusion by making the makefiles
behave like they read.

Change-Id: Ia141dc1e5a3892bb344f319fc3d573e0ce160352
diff --git a/Android.mk b/Android.mk
index e963f99..79ff490 100644
--- a/Android.mk
+++ b/Android.mk
@@ -1,7 +1,7 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := user
+LOCAL_MODULE_TAGS := optional
 
 # Only compile source java files in this apk.
 LOCAL_SRC_FILES := $(call all-java-files-under, src)