services: add drop weird binary-exists condition

services: add drop weird binary-exists condition

The package that ships the service is the same as the one that ships
the binaries, so quite the useless check and a remainder from initial
switch from sysv to systemd in ~2015 (when it was not 100% clear
what/how systemd features should be integrated or units encoded).

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>