Remove dreambooth Git link

[charliermarsh]

Summary

examples/boft_dreambooth/data/dreambooth is declared as a submodule, but there's no .gitmodules mapping for it, so various Git operations will fail on the repo.

data is actually already .gitignored, so it seems reasonable to just remove this submodule entirely, since cloning the repo (which is handled by the training script) won't lead to a dirty Git history anyway.

The alternative solution is to add a .gitmodules entry:

[submodule "dreambooth"]
    path = examples/boft_dreambooth/data/dreambooth
    url = https://github.com/google/dreambooth

The downside here is that you'll now be downloading the dataset whenever someone performs a recursive clone on the repo, which seems not to be the intent, since you're downloading the repo out-of-band from Git via the training script anyway.

[HuggingFaceDocBuilderDev]

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[BenjaminBossan]

Thanks for fixing this. This example was originally structured differently so that it used the sub-module. Later, that was changed, but this wasn't cleaned up.