docs(firewall): remove that ufw is shipped with Debian

I'm not sure if it did in the past, but as of Debian Trixie (13) ufw is certainly not preinstalled. Debian comes with nftables and recommends firewalld as a frontend for it.

ufw is available on Debian repos and is documented on the wiki, but not preinstalled.

See: https://wiki.debian.org/nftables

content/manuals/engine/network/packet-filtering-firewalls.md

@@ -90,9 +90,9 @@ forwarding from `ANY` zone to the `docker` zone.
 ## Docker and ufw
 
 [Uncomplicated Firewall](https://launchpad.net/ufw)
-(ufw) is a frontend that ships with Debian and Ubuntu,
-and it lets you manage firewall rules. Docker and ufw use firewall rules in
-ways that make them incompatible with each other.
+(ufw) is a frontend that ships with Ubuntu, and it lets you manage firewall
+rules. Docker and ufw use firewall rules in ways that make them incompatible
+with each other.
 
 When you publish a container's ports using Docker, traffic to and from that
 container gets diverted before it goes through the ufw firewall settings.