openssh: disable fail2ban

We've always had password authentication disabled, so it's not really
doing much except periodically locking us out of our own servers when we
misconfigure something

common/openssh.nix

@@ -8,6 +8,4 @@
       PermitRootLogin = "no";
     };
   };
-
-  services.fail2ban.enable = true;
 }