fix: remove dead reference to non-existent module .file_utils

[anzzyspeaksgit]

Summary

Removed the dead reference to the non-existent .file_utils module in gpt2_tokenization.py as requested.

Problem

Closes #1077

Solution

The from_pretrained method in GPT2Tokenizer previously attempted to import cached_path from .file_utils (a remnant of old huggingface/transformers code). Because .file_utils does not exist in the flagscale.train.megatron.training.tokenizer module, it could cause ImportError / EnvironmentError. I removed the try-except block entirely to keep the tokenizer loading strictly local vocabulary files cleanly.

Testing

• Verified pytest does not break by missing imports.

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This PR was created with AI assistance.

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