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: I137789faf6ad58669ea49c8eaaa05e62fd5e9835
diff --git a/Android.mk b/Android.mk
index 704bbbc..1a7f6a9 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
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files)