systemd: fix dbus activation

Various DBus activated services fail to start with errors similar to:

  Unit dbus-org.freedesktop.hostname1.service failed to load: File exists.

The message itself is rather vague and can be seen as a warning in
systemd-networkd logs. Meanwhile, tools like hostnamectl don't work
at all.

The post-install target hook SYSTEMD_SANITIZE_PATH_IN_UNITS was replacing
symlinks with duplicate files. The find command could have used -type f
to avoid this but I instead chose to remove the hook since this fix doesn't
seem to be needed anymore.

Signed-off-by: Gabe Evans <gabe@hashrabbit.co>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>