misc: rm unused model_loader

[zhyncs]

Motivation

While reviewing the code, it was discovered that this section of code is not being used and seems to have been broken up. For example, in python/sglang/srt/model_loader/utils.py, from sglang.srt.layers.quantization import get_quantization_config, but actually there is no quantization file under the layers directory anymore. This should be due to incomplete deletion previously.

Modification

Checklist

• Before submitting a PR for review, make sure it has passed verification in your local development environment at least.
• Ensure pre-commit pre-commit run --all-files or other linting tools are used to fix potential lint issues.
• Confirm that modifications are covered by complete unit tests. If not, please add more unit tests for correctness.
• Modify documentation as needed, such as docstrings or example tutorials.