MRPC test set differences between torch and tensorflow datasets
Realized that `tensorflow_datasets` is not provided by Huggingface and should therefore raise the issue there.
## Describe the bug
When using `load_dataset("glue", "mrpc")` to load the MRPC dataset, the test set includes the labels. When using `tensorflow_datasets.load('glue/{}'.format('mrpc'))` to load the dataset the test set does not contain the labels. There should be consistency between torch and tensorflow ways of importing the GLUE datasets.

## Steps to reproduce the bug

Minimal working code  
```python
from datasets import load_dataset
import tensorflow as tf
import tensorflow_datasets

# torch
dataset = load_dataset("glue", "mrpc")
# tf
data = tensorflow_datasets.load('glue/{}'.format('mrpc'))
data = list(data['test'].as_numpy_iterator())
for i in range(40,50):
  tf_sentence1 = data[i]['sentence1'].decode("utf-8") 
  tf_sentence2 = data[i]['sentence2'].decode("utf-8") 

  tf_label = data[i]['label']
  
  index = data[i]['idx']
  print('Index {}'.format(index))
  torch_sentence1 = dataset['test']['sentence1'][index]
  torch_sentence2 = dataset['test']['sentence2'][index]

  torch_label = dataset['test']['label'][index]
  print('Tensorflow: \n\tSentence1 {}\n\tSentence2 {}\n\tLabel {}'.format(tf_sentence1, tf_sentence2, tf_label))
  print('Torch: \n\tSentence1 {}\n\tSentence2 {}\n\tLabel {}'.format(torch_sentence1, torch_sentence2, torch_label))
```

Sample output  
```
Index 954
Tensorflow: 
	Sentence1 Sabri Yakou , an Iraqi native who is a legal U.S. resident , appeared before a federal magistrate yesterday on charges of violating U.S. arms-control laws .
	Sentence2 The elder Yakou , an Iraqi native who is a legal U.S. resident , appeared before a federal magistrate Wednesday on charges of violating U.S. arms control laws .
	Label -1
Torch: 
	Sentence1 Sabri Yakou , an Iraqi native who is a legal U.S. resident , appeared before a federal magistrate yesterday on charges of violating U.S. arms-control laws .
	Sentence2 The elder Yakou , an Iraqi native who is a legal U.S. resident , appeared before a federal magistrate Wednesday on charges of violating U.S. arms control laws .
	Label 1
Index 711
Tensorflow: 
	Sentence1 Others keep records sealed for as little as five years or as much as 30 .
	Sentence2 Some states make them available immediately ; others keep them sealed for as much as 30 years .
	Label -1
Torch: 
	Sentence1 Others keep records sealed for as little as five years or as much as 30 .
	Sentence2 Some states make them available immediately ; others keep them sealed for as much as 30 years .
	Label 0
```

## Expected results
I would expect the datasets to be independent of whether I am working with torch or tensorflow.

## Actual results
Test set labels are provided in the `datasets.load_datasets()` for MRPC. However MRPC is the only task where the test set labels are not -1.

## Environment info
- `datasets` version: 1.7.0
- Platform: Linux-5.4.109+-x86_64-with-Ubuntu-18.04-bionic
- Python version: 3.7.10
- PyArrow version: 3.0.0
