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: Iee9c5506b89fcb4375291cf0a6236b705f579dce
diff --git a/Android.mk b/Android.mk
index 979bdce..0b9a9d6 100644
--- a/Android.mk
+++ b/Android.mk
@@ -11,7 +11,7 @@
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := user
+LOCAL_MODULE_TAGS := optional
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files)