Remove rebundant code

understand_sentiment/README.en.md

@@ -314,12 +314,6 @@ train_reader = paddle.batch(
 
 test_reader = paddle.batch(
     lambda: paddle.dataset.imdb.test(word_dict), batch_size=100)
-
-trainer.train(
-    reader=train_reader,
-    event_handler=event_handler,
-    feeding=feeding,
-    num_passes=2)
 ```
 
 `feeding` is devoted to specifying the correspondence between each yield record and `paddle.layer.data`. For instance, the first column of data generated by `paddle.dataset.imdb.train()` corresponds to `word` feature.