Remove image_transforms functions from init

[amyeroberts]

What does this PR do?

Removes functions in the image_transforms library from src/transformers/_init__.py.

The functionality this module provides are utils for processing images and are not the primary goal of the library.

Address an issue raised in #20627 - which highlighted some functions were in the init and others weren't.

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[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[sgugger]

Thanks!

[ydshieh]

👍 💯