Remove transforms from public decoder API

[Dan-Flores]

This PR removes transforms from the public _video_decoder.py API. To be certain, the torchcodec.transforms imports are removed.

• test/test_transform_ops.py is deleted
• The docs reference to transforms and its uses are deleted

The implementations in https://github.com/meta-pytorch/torchcodec/blob/main/src/torchcodec/transforms/_decoder_transforms.py and corresponding __init__.py are not deleted, as they are private classes, and cannot be used in _video_decoder.py after these changes.

[NicolasHug]

This LGTM if CI is green, thanks @Dan-Flores . I'll approve but it's worth waiting for @scotts 's input

[scotts]

I think we should still remove this entire file:

torchcodec/src/torchcodec/transforms/__init__.py

Line 7 in f2c8c69

from ._decoder_transforms import DecoderTransform, Resize # noqa

If we don't, users will still be able to see torchcodec.transforms and the two classes it exposes. And then I think we need to remove transforms from the top-level init:

torchcodec/src/torchcodec/__init__.py

Line 12 in f2c8c69

from . import decoders, encoders, samplers, transforms # noqa

[scotts]

Thanks, I think we have successfully removed external evidence of my recent efforts from the next release. :)