nixos/tests/rancher: remove k3s check-config

`k3s check config` fails due to the check script expecting
`IP_NF_FILTER`, `IP_NF_NAT` and `IP_NF_TARGET_MASQUERADE`. However,
these options are considered legacy in Linux 6.18 (the current default
in nixpkgs).

When/if upstream adapts the check script, it can be added to the tests
again.

nixos/tests/rancher/multi-node.nix

@@ -218,11 +218,6 @@ in
       # wait for the agent to show up
       server.wait_until_succeeds("kubectl get node agent")
 
-      ${lib.optionalString (rancherDistro == "k3s") ''
-        for m in machines:
-            m.succeed("k3s check-config")
-      ''}
-
       server.succeed("kubectl cluster-info")
       # Also wait for our service account to show up; it takes a sec
       server.wait_until_succeeds("kubectl get serviceaccount default")

nixos/tests/rancher/single-node.nix

@@ -84,9 +84,6 @@ in
       machine.wait_for_unit("${serviceName}")
       machine.succeed("kubectl cluster-info")
       machine.fail("sudo -u noprivs kubectl cluster-info")
-      ${lib.optionalString (rancherDistro == "k3s") ''
-        machine.succeed("k3s check-config")
-      ''}
 
       # Also wait for our service account to show up; it takes a sec
       machine.wait_until_succeeds("kubectl get serviceaccount default")