Remove docs makefile tag, since the build system doesn't use it.

The docs tag got removed from almost all locations months ago,
but this location didn't get updated (probably because there were
two instances in this file.

This'll save some confusion.

Change-Id: I977939130db0364844710c47b93e8d729b97d3ef
diff --git a/java-jni/Android.mk b/java-jni/Android.mk
index a09af4b..49b8862 100644
--- a/java-jni/Android.mk
+++ b/java-jni/Android.mk
@@ -22,7 +22,7 @@
 # ============================================================
 include $(CLEAR_VARS)
 
-LOCAL_MODULE_TAGS := docs
+LOCAL_MODULE_TAGS := optional
 
 LOCAL_SRC_FILES:= \
 	j_neo_util.c \