Change systemd service location

Units of installed packages belong in /usr/lib/systemd/system
http://www.freedesktop.org/software/systemd/man/systemd.unit.html

Signed-off-by: Michael Buesch <m@bues.ch>
uninstall.sh: Fix removal of symbolic links

Signed-off-by: Michael Buesch <m@bues.ch>