package/tor: do not install systemd service file

Upstream removed the sample service file for use with systemd:
https://gitweb.torproject.org/tor.git/commit/contrib?h=maint-0.4.5&id=915af1a65bc217fa33490876199bb69f760bea23

Fixes:
http://autobuild.buildroot.net/results/b80/b807f19283528b9f0d0c46250b660ea84695679c/
http://autobuild.buildroot.net/results/de4/de4f1a99b1c524b81579ee804156e26d3f8babe7/



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>