[chore] fix: retain memory utility.

[sayakpaul]

What does this PR do?

My bad that in

diffusers/src/diffusers/training_utils.py

Line 263 in 534848c

def clear_objs_and_retain_memory(objs: List[Any]):

I assumed that the scope of del would carry forward but that is not the case. So, even when we call del obj it actually just deletes the local reference, it doesn't carry forward. So, we're better off without it and doing del explicitly (like the changes done in this PR).

Thanks to @a-r-r-o-w for catching this. It didn't go to a release yet, so, I think this shouldn't have any issues.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[a-r-r-o-w]

Lightning fast fix, thanks! I'm not sure about the name retain_memory though, as retain means to keep something as-is. Maybe free_memory or something would be better? No problem if not though

[sayakpaul]

I had a different meaning in mind, don't know why. But I get your point. Will rename to free_memory() as it makes more sense, of course.