Clean up TX clean up

In AppLayerTransactionsCleanup instead of figuring out 'done' tx id's
itself, now call AppLayerTransactionGetActive for both directions to
figure out the completed TX id's.

https://buildbot.suricata-ids.org/builders/inliniac/builds/85
https://buildbot.suricata-ids.org/builders/inliniac-pcap/builds/6