sshguard: do not create ipset in post-start

Upstream switched to a different type of ipset table, whereas we
create ipset in post-start which overrides upstream, and renders
sshguard ineffective.

Remove ipset creation from post-start, and let it get automatically
by upstream script (sshg-fw-ipset) as part of startup

nixos/modules/services/security/sshguard.nix

@@ -107,8 +107,6 @@ in {
       path = with pkgs; [ iptables ipset iproute systemd ];
 
       postStart = ''
-        ${pkgs.ipset}/bin/ipset -quiet create -exist sshguard4 hash:ip family inet
-        ${pkgs.ipset}/bin/ipset -quiet create -exist sshguard6 hash:ip family inet6
         ${pkgs.iptables}/bin/iptables  -I INPUT -m set --match-set sshguard4 src -j DROP
         ${pkgs.iptables}/bin/ip6tables -I INPUT -m set --match-set sshguard6 src -j DROP
       '';