[VLM] Remove image_input_type from VLM config

[xwjiang2010]

Remove support for pixel_values and image_features.

User facing API is updated to be multi_modal_data = {"image": image}. See docs/source/models/vlm.rst.
Remove MultiModalData completely.

See #4194 for context.

cc @ywang96 @DarkLight1337

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[DarkLight1337]

This is to prevent accidental merge until v0.5.1 has been released.

[DarkLight1337]

I've left another round of comments, PTAL.

[DarkLight1337]

Another round of comments! I think this PR is almost ready for merge.

[ywang96]

Left a few comments - PTAL!

[ywang96]

Good catch! Did you observed a memory leak from not having this?

[xwjiang2010]

nope, it will just complain about missing fp. I guess @DarkLight1337 also saw something similar so he added image.load() in ImageData initialization.

[ywang96]

LGTM - Thank you for the work!

🚢