Refactor TFP call to just sigmoid()

[Rocketknight1]

We're seeing issues caused by Tensorflow Probability + Keras 3 incompatibilities. Annoyingly, these are being thrown even when people are trying to use unrelated Torch models, as long as they have TF / TFP installed!

The underlying cause is that we import TFP in one of our pipeline files if it's present, and this file is run when pipeline is imported, even if the user is using an entirely different pipeline/framework. I removed the import entirely - it was only used to get the probabilities of a Bernoulli distribution given input logits, but this is just the sigmoid function, so I replaced the whole thing with a single call to sigmoid() instead.

[amyeroberts]

Much better 🧘 Thanks!

[HuggingFaceDocBuilderDev]

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