test: use cancelation from ktesting

The return type of ktesting.NewTestContext is now a TContext. Code
which combined it WithCancel often didn't compile anymore (cannot overwrite
ktesting.TContext with context.Context). This is a good thing because all of
that code can be simplified to let ktesting handle the cancelation.

test/integration/framework/test_server.go

@@ -59,6 +59,7 @@ type TestServerSetup struct {
 type TearDownFunc func()
 
 // StartTestServer runs a kube-apiserver, optionally calling out to the setup.ModifyServerRunOptions and setup.ModifyServerConfig functions
+// TODO (pohly): convert to ktesting contexts
 func StartTestServer(ctx context.Context, t testing.TB, setup TestServerSetup) (client.Interface, *rest.Config, TearDownFunc) {
 	ctx, cancel := context.WithCancel(ctx)