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: Ia90c376d627c6c9faeccf040695b88bb32779f82

Android.mk

 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := user
+LOCAL_MODULE_TAGS := optional
 
 LOCAL_SRC_FILES := $(call all-subdir-java-files)