Remove firewalld services, since they are part of firewalld now.

The firewalld services files (for privoxy, tor-socks, xmpp-bosh, xmpp-client, and xmpp-server) have been added to firewalld [1]. But there's a conflict now between the plinth and firewalld packages in Debian [2]. Since the files are maintained in firewalld now, there's no need to keep them in plinth.

[1] https://fedorahosted.org/firewalld/ticket/13
[2] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=750927