Remove declaration of unused function.

The function ReceiveAFP() is declared, but never defined, so removed it.

Simple clean noticed while reading the file.

tests passed with PR script.
https://buildbot.suricata-ids.org/builders/ken-tilera/builds/119
https://buildbot.suricata-ids.org/builders/ken-tilera-pcap/builds/53

@regit - This is your code, so you might want to double check.