[configs/releng] Use dhcpcd service provided by the package.

Implements FS#34075.

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

configs/releng/root-image/etc/systemd/system/dhcpcd.service

-[Unit]
-Description=dhcpcd on all interfaces
-Wants=network.target
-Before=network.target
-
-[Service]
-Type=forking
-PIDFile=/run/dhcpcd.pid
-ExecStart=/sbin/dhcpcd -A -b -q
-ExecStop=/sbin/dhcpcd -k
-
-[Install]
-WantedBy=multi-user.target