libct/cg/sd: TestFreezePodCgroup: rm explicit freeze

This was initially added by commit 3e5c199708 because Set (with
r.Freezer = Frozen) was not able to freeze a container.

Now (see a few previous commits) Set can do the freeze, so the explicit
Freeze is no longer needed.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/cgroups/systemd/systemd_test.go

@@ -219,9 +219,6 @@ func TestFreezePodCgroup(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if err := pm.Freeze(configs.Frozen); err != nil {
-		t.Fatal(err)
-	}
 	if err := pm.Set(podConfig.Resources); err != nil {
 		t.Fatal(err)
 	}