android: remove LOCAL_MODULE_TAGS := optional tag

Seems to be the default option since ~2009 with commit 2f31293ba78 "auto
import from //branches/cupcake/...@137197". Fleshed out from a larger
commit in the AOSP repo/fork.

Cc: Dan Willemsen <dwillemsen@google.com>
Cc: Chih-Wei Huang <cwhuang@android-x86.org>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>