Use Pytorch Lightning's LightningDataModule

[nateraw]

🚀 Feature

Refactor to reflect the built-in LightningDataModule that has been implemented directly into lightning by removing the same code here and replacing with references to pl.LightningDataModule

Motivation

Pytorch Lightning version 0.9.0 implements the LightningDataModule directly in lightning. We have no need for the bolts implementation once that version is released, so we should update the code here accordingly.

Pitch

I suggest we merge a fix for this as soon as the stable version of 0.9.0 has been released. We could do it earlier, but something bothers me about having a prerelease in requirements.txt 😅

Alternatives

Additional context

The implementation is nearly the same and should cause no conflicts.

• The code can be found here
• The docs can be found here

[github-actions]

Hi! thanks for your contribution!, great first issue!