How are `prep_classification` and `prep_training` different?

[sfmig]

In a PR discussion with @alessandrofelder, we noticed these two functions seem to only vary in the order of their input parameters:

• prep_classification definition
• prep_training definition

If both classification and training require the same setup, maybe we can combine them in one function and name it prep_tensorflow_and_model or similar?

[Adam Tyson]

Yep, no reason to have both of these. Should just check that they aren't used in cellfinder/cellfinder-napari.