[k8s.io/apimachinery/pkg/test]: cleanup commented code

The commented code has no help to make reader more comprehensiable, it was just
a legacy copy paste.

Signed-off-by: Zhou Peng <p@ctriple.cn>

staging/src/k8s.io/apimachinery/pkg/test/runtime_serializer_protobuf_protobuf_test.go

@@ -223,8 +223,6 @@ func TestProtobufDecode(t *testing.T) {
 		0x22, 0x00, // content-encoding
 	}
 
-	//err1 := fmt.Errorf("a test error")
-
 	testCases := []struct {
 		obj   runtime.Object
 		data  []byte