🚨🚨🚨 [`Blip`] remove labels masking
# What does this PR do?

Addresses https://github.com/huggingface/transformers/pull/23004#issuecomment-1523776082

This PR aims to harmonize the training procedure for most of recent additions in `transformers`. It should be users' responsibility to fill_mask the padding tokens of the labels with the correct value. This PR addresses the issue that was raised by other architectures such as Luke or Pix2Struct

However I realize that even if this patch is applied, we still mask fill the labels with -100 [here](https://github.com/huggingface/transformers/blob/9435cc6670b7b8656b33e8ff28d3bbe9bafbca9d/src/transformers/models/blip/modeling_blip.py#L1133), similarly as in [T5](https://github.com/huggingface/transformers/blob/9435cc6670b7b8656b33e8ff28d3bbe9bafbca9d/src/transformers/models/t5/modeling_t5.py#L868)

I would love your feedback on this, @amyeroberts !

_The documentation is not available anymore as the PR was closed or merged._