"Flags" is really a redundant length field

Props to huin on the Artemis forums for discovering this:
http://artemis.forumchitchat.com/post/show_single_post?pid=1280696012&postcount=34

All references to flags have been removed. Confirming that the
"remaining bytes" field is correct is now part of the incoming packet
validation. Outgoing packets have this field computed automagically.