Seq2seq finetune example: "Please save or load state of the optimizer"
When running the example scripts in examples/seq2seq/finetune_bart and finetune_t5, get warning messages:

## Environment info
- `transformers` version: 3.3.1
- Platform: Linux-4.15.0-66-generic-x86_64-with-glibc2.10
- Python version: 3.8.5
- PyTorch version (GPU?): 1.6.0 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: Ran both with and without gpus; same result
- Using distributed or parallel set-up in script?: no

### Who can help
@sshleifer  for examples/seq2seq, Bart
@patrickvonplaten (maybe because this also happens in T5?) 

## Information
Model I am using (Bert, XLNet ...):
Occurs when running bart and also when running T5 via the examples/seq2seq/finetune

The problem arises when using:
* [X] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [X ] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:
Steps to reproduce:
1) clone transformers into new directory
2) Set up environment (new): cd transformers && pip install .e; cd examples && pip install -r requirements.txt
3) cd seq2seq && ./finetune_t5_bart_tiny.sh

Observe that warnings are printed:

../python3.8/site-packages/pytorch_lightning/utilities/distributed.py:37: UserWarning: Could not log computational graph since the `model.example_input_array` attribute is not set or `input_array` was not given 
warnings.warn(*args, **kwargs)
.../python3.8/site-packages/torch/optim/lr_scheduler.py:200: UserWarning: Please also save or load the state of the optimzer when saving or loading the scheduler.
  warnings.warn(SAVE_STATE_WARNING, UserWarning)

(There is both the optimizer warning and the computational graph logging warning)


## Expected behavior

Should not see warnings for the given example.

## Other notes:
There was a related issue where supplementary files / checkpoints were not being saved, but that seems to be fixed now.
I'll leave it to @sshleifer - haven't really used the seq2seq fine-tuning too much.

Maybe @patil-suraj has also an idea here :-) <|||||>You can safely ignore the `lr_scheduler` warning. `optimzer` is saved, but torch `lr_scheduler` warns you anyway just so you don't forget.

Not sure about the first warning, but you can also safely ignore that
<|||||>@patil-suraj Thank you! Would there be an easy way to somehow silence the warning, or print a logging statement from huggingface library that the warning can be safely ignored? <|||||>I believe this warning has been hidden on the `master` branch, and will be hidden in the next release. See [this](https://github.com/huggingface/transformers/blob/master/src/transformers/trainer_pt_utils.py#L114-L119).<|||||>Cool! Looks like originally in #7401. I pulled master and confirmed that this is fixed. 

Any notes on the computational graph warning that also pops up?
../python3.8/site-packages/pytorch_lightning/utilities/distributed.py:37: UserWarning: Could not log computational graph since the model.example_input_array attribute is not set or input_array was not given