slapos.cfg.example: Drop firewalld pid

It's not used by us (controlled by supervisor), and would escape /opt/slapos
anyway.

slapos.cfg.example

@@ -38,7 +38,7 @@ use_unique_local_address = False
 # to enable, change to [firewall]
 [disabled-firewall]
 dbus_executable = /opt/slapos/parts/dbus/bin/dbus-daemon --nofork --nopidfile --system
-firewall_executable = /opt/slapos/parts/firewalld/sbin/firewalld --nofork --log-file /opt/slapos/log/firewalld-process.log
+firewall_executable = /opt/slapos/parts/firewalld/sbin/firewalld --nofork --nopid --log-file /opt/slapos/log/firewalld-process.log
 firewall_cmd = /opt/slapos/parts/firewalld/bin/firewall-cmd
 reload_config_cmd = slapos node restart firewall
 log_file = /opt/slapos/log/firewalld.log